CHAPTER VII_The nutrition of man

THE EFFECT OF LOW PROTEID DIET ON HIGH PROTEID ANIMALS

TOPICS: A wide variety of foods quite consistent with temperance in

diet. Safety of low proteid standards considered. Arguments based

on the alleged effects of low proteid diet on high proteid animals.

Experiments of Immanuel Munk with dogs. Experiments of Rosenheim.

Experiments of Jägerroos. Comments on the above experiments. The

experiments of Watson and Hunter on rats. The writer’s experiments

with dogs. Details of the results obtained with six dogs. Comparison

of the results with those of previous investigators. Effect of a

purely vegetable diet on dogs. Different nutritive value of specific

proteids considered. Possible influence of difference in chemical

constitution of individual proteids. Effect of low proteid diet on

the absorption and utilization of food materials in the intestine

of dogs. General conclusions from the results of experiments with

animals.

Man is by choice an omnivorous creature; he reaches out ordinarily in

all directions for as wide a variety of foods as his circumstances and

surroundings will allow. He rightly cultivates a taste for foods that

have individuality of flavor, and derives pleasure and satisfaction

from the eating of delicacies that appeal to palate and to reason.

All this he can do without becoming an epicure or a glutton, and

without violation of physiological laws or disregard of the teachings

of temperance. As a being endowed with reason and intelligence he is,

however, necessarily mindful of the possible deleterious effect of

undue quantities of food, as he is likewise mindful of the desirability

of avoiding certain varieties of food which personal experience has

taught him are fraught with possible danger. Care and prudence in diet

are legitimate outcomes of a reasonable interest in the welfare of the

body, upon which so largely depend the happiness and working power of

the individual.

The adoption of dietary habits that aim to accord with the

physiological requirements of the body does not compel a crucifying of

the flesh or a disregard of personal likes and dislikes. A reasonable

intelligence combined with a disposition to exercise the same degree

of judgment and care in the nutrition of the body as is expended on

other matters, of no greater importance, pertaining to the individual,

to the household, or to business interests, are all that is needed to

bring about harmony between every-day dietary habits and the nutritive

requirements of the body. There is no occasion, unless one finds

pleasure and satisfaction in so doing, to resort to a limited dietary

of nuts and fruits, to become an ardent disciple of vegetarianism,

to adopt a cereal diet, to abjure meats entirely, or to follow in an

intensive fashion any particular dietary hobby, except so far as may

be necessary to insure an adequate amount of non-nitrogenous foods to

meet the energy requirements of the body without unduly increasing

the intake of proteid or nitrogenous food. Naturally, a man leading

a life of great physical activity with the consequent demand for a

large energy-yielding intake will be compelled to resort largely to

vegetable foods, rich in starch and poor in proteid, or to eat largely

of fatty foods. Reliance on meats and animal foods in general, under

such conditions, would plainly involve a high proteid intake with a

consequent high nitrogen metabolism, with the chance that even then the

energy requirement would not be fully met.

In view of all that has been said, reinforced by the various facts

brought forward as evidence, we must recognize the value of the

non-nitrogenous foods as a source of energy, and this means plainly

food from the plant kingdom. In any rational diet, vegetable foods of

low nitrogen-content must predominate, while animal foods with their

higher nitrogen values must be greatly subordinate in amount, if the

nitrogen or proteid metabolism of the body is to be maintained at a

level commensurate with true physiological requirements. But there

comes the ever-recurring question, Are the lower proteid standards

quite safe to follow? Are we warranted in turning aside from the

teachings based on the habits and customs of mankind? Many reasons have

already been presented which seemingly justify an affirmative answer,

while the experimental results and the observations on various groups

of people, covering years of time, speak with no uncertainty regarding

the element of safety, and indicate clearly that the absolute proteid

requirement of the body is quite small; much smaller indeed than

the amount of proteid food consumed by the average individual would

seemingly imply.

Probably the most striking evidence, certainly of an experimental

nature, so far presented against the safety of a relatively low

proteid diet for man is that based on the results of several studies

made to ascertain the effect of a reduced proteid intake on so-called

high proteid animals. Animal kind may be divided into three groups

according to the nature of their food, viz., high proteid feeders, such

as carnivorous animals in general, of which the dog is a good type;

omnivorous or moderate proteid consumers, to which class man belongs;

and low proteid consumers, such as herbivorous animals. Three series of

experiments have been reported by independent workers on the effects of

reducing the amount of proteid food in the diet of dogs. The results

of these experiments were of such a character that it has come to be

understood that animals of this type cannot exist for any great length

of time on a low proteid diet. It is affirmed that in a relatively

short period the animals reach such a state that they either die, or

are in such poor condition that they must be fed a more liberal amount

of proteid to maintain them alive. The explanation offered is that the

low proteid diet results “in a loss of the power of absorption from the

intestinal tract, caused apparently by a change in the condition of the

epithelial cells, as well as by a diminished secretion of the digestive

juices.”

The argument based on this evidence is that while a high proteid animal

feels at once, or almost immediately, the deleterious effect of a

reduction in the amount of proteid food, an omnivorous animal may be

more tardy in manifesting the injurious action, which, however, is sure

to follow sooner or later from any material reduction of proteid below

the customary standards. In other words, man as a moderate proteid

consumer can endure for a time even large reductions in the amount

of proteid food, but eventually there will be manifested some of the

disastrous results obtained with dogs. Here, we have a somewhat serious

indictment, one that merits careful consideration. To be sure, it may

be objected that between dog and man there is a wide gulf, and that

there is no justification for assuming that these two types of animal

life have anything in common. Still, the experience of many years

has taught the physiologist that much light can be thrown upon the

processes of higher types of life by a study of what occurs in lower

forms, and on the subject of nutrition any one of experience would

hesitate to cast out of court the evidence gathered from observation of

what occurs among the higher animals. It will be the part of wisdom,

therefore, to scrutinize somewhat carefully the character of this

evidence obtained from a study of the behavior of dogs toward a low

proteid diet.

The first series of experiments was made in 1891 by the late Immanuel

Munk of Berlin, privat docent of physiology at the University, followed

by further experiments in 1893.[68] Four dogs in all were studied. The

diet made use of was “fleischmehl” (dried meat ground to a powder),

fat (suet), and rice boiled together with water. We may refer briefly

to the details of one experiment. The dog weighed 10.4 kilograms, and

at first was given a daily diet composed of 85 grams of rice, 29 grams

of fat, and 30 grams of the flesh meal. This ration contained 30.3

grams of proteid, 31 grams of fat, and 66 grams of carbohydrate, with

a total fuel value of 663 calories, or 63 calories per kilogram of

body-weight. On this diet, there was at the outset a slight loss of

body-weight, after which both body equilibrium and nitrogen equilibrium

were practically maintained. After this preliminary period of three

weeks, the day’s diet was altered by replacing 15 grams of the proteid

by 15 grams of rice, so that the daily ration consisted of 15.3 grams

of proteid (with 2.42 grams of nitrogen), 31 grams of fat, and 81 grams

of carbohydrate, with essentially the same fuel value per kilo of

body-weight as before. Later, the fuel value of the food was further

increased by raising the amount of rice to 125 grams per day, the day’s

ration then consisting of 15.5 grams of proteid, 37 grams of fat, and

96 grams of carbohydrate, with a total fuel value of 780 physiological

heat units, or 78 calories per kilo. On this diet, nitrogen equilibrium

was maintained and the animal gained somewhat in body-weight. By the

seventh week, however, Munk reports that the animal began to show

signs of change; there was loss of appetite, absorption of the daily

food was impaired, both proteid and fat failing in large degree to be

utilized, while nitrogen equilibrium could no longer be maintained.

This condition continued during the next week, aggravated by vomiting

and accompanied by loss of strength and vigor. At the beginning of

the tenth week of this low proteid ration, the animal was in a very

poor condition, with complete loss of appetite, little inclination to

take food, etc. On feeding a liberal diet of fresh meat, as much as

250 grams per day, with some fat (50 grams a day), the animal speedily

recovered its appetite, and in a short time was in normal condition,

absorption of food and utilization of the same being as complete as at

the beginning of the experiment.

[68] Ueber die Folgen einer ausreichenden, aber eiweissarmen Nahrung.

Ein Beitrag zur Lehre vom Eiweissbedarf. Virchow’s Archiv für

pathologische Anatomie und Physiologie, Band 132, p. 91.

It is not necessary to give further details bearing on the three

additional experiments. It will suffice to quote the general

conclusions which Munk drew from the various results obtained, viz.,

that a low proteid intake in the case of dogs causes a loss of

appetite, weakness, vomiting, etc., while body-weight and nitrogen

equilibrium are difficult or impossible to maintain. More specifically,

Munk’s observations led him to state that for dogs of ten kilograms

body-weight a daily intake of 0.255 gram of nitrogen per kilo of

body-weight is not sufficient to maintain the normal condition of the

body, even when the fuel value of the day’s food amounts to more than

100 calories per kilo. In order to have the animal continue in nitrogen

and body equilibrium, the daily food must contain at least 0.31 gram of

nitrogen per kilogram of body-weight, with sufficient non-nitrogenous

food to yield over 100 calories per kilo.

Let us now pass to the experiments made by Rosenheim,[69] which were

carried on at about the same date as Munk’s. In the first experiment,

the dog weighed 11.3 kilograms, and was fed daily a low proteid ration

having a fuel value of 1447 calories and containing 2.825 grams of

nitrogen. This ration was reduced in a short time to a still lower

plane, viz., to 1066 calories and 2.525 grams of nitrogen daily. The

food as then given was composed of 170 grams of rice, 50 grams of

fat, and 25 grams of chopped meat, on which the dog gained weight and

preserved nitrogen equilibrium. For six weeks, or thereabouts, the

animal maintained its normal condition, after which it began to show

symptoms of a general disturbance, with lack of appetite and weakness

accompanied by a condition of icterus. Addition of meat extract to

the diet to improve the flavor was without any appreciable effect.

During the next two weeks, the condition of the animal steadily grew

worse, although the body-weight remained practically stationary and

nitrogen equilibrium was maintained. A week later, the animal died in

a condition of exhaustion, without having manifested any symptoms of

disturbed metabolism. There was found a marked catarrhal condition

of the mucous membrane of the gastro-intestinal tract, with a fatty

degeneration or metamorphosis of the glandular apparatus, but nothing

sufficiently specific to account for the peculiar manner of death.

[69] Theodor Rosenheim: Ueber den Gesundheitsschädigenden Einfluss

eiweissarmer Nahrung. DuBois-Reymond’s Archiv für Physiologie,

1891, p. 341. Also, Weiterer Untersuchungen über die Schädlichkeit

eiweissarmer Nahrung. Pflüger’s Archiv f. d. gesammte Physiologie,

Band 54, p. 61, 1893.

A second experiment with a dog of 5.8 kilograms, fed on meat, fat, and

rice, led to essentially the same results as the preceding experiment.

At the end of the first month, there appeared indications that the

animal was not well, loss of appetite being marked, with disturbance

of the stomach accompanied by occasional vomiting. These symptoms

disappeared quickly when the animal was given for a few days large

quantities of meat. On returning to the original low proteid diet,

with its large content of rice, the symptoms gradually reappeared.

At the end of two months the animal had again lost its appetite, and

before the end of the fifth month the subject was dead. Post-mortem

examination showed especially a strong fatty degeneration of the

epithelial cells of the mucous membrane of the stomach and intestine.

Rosenheim concludes that a diet poor in proteid is unhealthful for

dogs, and that a daily ration containing even 0.32 gram of nitrogen

per kilogram of body-weight, and with a fuel value of 110 calories per

kilo, is not sufficient to maintain the animal in a condition of health.

The next series of experiments was made by Jägerroos[70] of Finland.

This investigator was evidently impressed by the unfavorable and

monotonous character of the diet made use of by the preceding

investigators, and sought to introduce a little variety, recognizing

also that with a carnivorous animal it is difficult to reduce the

proteid to a low level and maintain the necessary fuel value, without

introducing foodstuffs to which the animal is wholly unaccustomed. In

the first experiment, the dog had a body-weight of 5.77 kilograms, and

at the beginning was fed daily 40 grams of meat and 100 grams of sugar,

equal to 0.31 gram of nitrogen and 80 calories per kilo of body-weight.

The experiment continued for eight months, sugar being replaced in part

by butter, and occasionally bread, fat, and wheat meal being used in

proper amount to yield the given nitrogen and fuel values. During the

last five months, the intake of nitrogen per day averaged 0.29 gram

per kilo, with a fuel value amounting to 89 calories daily per kilo of

body-weight. During this period, the animal maintained a plus nitrogen

balance for a large part of the time. The experiment was then continued

for two months longer, with a gradual diminution in the nitrogen of the

food and in the fuel value, the animal dying at the end of the tenth

month.

[70] B. H. Jägerroos: Ueber die Folgen einer ausreichenden, aber

eiweissarmen Nahrung. Skandinavisches Archiv für Physiologie, Band

13, p. 375, 1902.

In a second experiment, the dog made use of weighed at the beginning

11.97 kilograms. During the first five months, the average intake of

nitrogen amounted daily to 0.29 gram per kilo, while the average fuel

value of the food (meat, fat, and sugar) was 76 calories per kilo

daily. In the middle of the seventh month the animal was quite ill,

with poor appetite, vomiting, etc. Body-weight began to fall off, and

the animal soon died. With both of these animals, the experiment ended

suddenly by a sharp and short illness.

Jägerroos, however, believed that both animals died from a severe

case of infection, and not as the result of the diminished intake of

proteid. This view was fully substantiated, in his opinion, by the

evidence furnished on bacteriological and morphological examination.

There was no pathological alteration and no fatty degeneration in the

intestinal epithelium; nothing to indicate any connection between the

lowered proteid intake and the death of the animal. To be sure, the

long-continued diet poor in nitrogen might have diminished the power

of resistance of the body, but no proof of this is offered. There

was indicated merely a simple infection, as shown by the presence

of Streptococcus and Bacterium coli communis in the blood. But, as

Jägerroos states, one might well conceive of a lowered power of

resistance on the part of the body, due not to any change in diet,

but to the long-continued confinement in a cage with the enforced

inactivity and lack of freedom. It is to be noted, furthermore, that

here there was no sign of a gradual and progressive weakening of

the body, no indication of any disturbance of the digestive tract

with diminished power of absorption of either fat or proteid. On the

contrary, there was a sudden and sharp attack of some infectious

disease by which the animals quickly succumbed. Jägerroos was of the

opinion that in the absence of this infection the animals would have

continued to live for a long period of time.

If a low proteid diet works so inimically on high proteid animals as

Munk and Rosenheim thought, it would naturally be expected that the

small proteid ration followed so long by Jägerroos would have resulted

in the appearance of marked symptoms, at least a gradual and persistent

falling off in body-weight, inability to maintain nitrogen equilibrium,

etc.; but none of these things occurred. In Munk’s first experiment,

the animal was given no fresh meat whatever during four weeks. Is it

not quite possible that in the abrupt cutting off of this wonted form

of food a disturbance may have been set up in the gastro-intestinal

tract, which paved the way for the more serious results that followed?

Jägerroos used only fresh, uncooked meat in his experiments, and laid

great stress upon the importance of not departing any more than was

necessary from the accustomed form of diet. The writer is strongly of

the opinion that sufficient stress has not been laid upon this phase of

the subject. A satisfactory diet for dog as for man must meet ordinary

hygienic requirements; it must not only be sufficient in amount, but

it must be easily digestible, of accustomed flavor, appealing to eye,

nostrils, and palate, with reasonable variation occasionally and of

moderate volume. With due regard to these conditions, I believe with

Jägerroos that not much attention need be paid to the proportion

of nitrogen therein, for however small the amount it will be found

sufficient to meet the needs of the body.

These are the results, collectively, so frequently used to point

a moral for man: Beware of the possible danger of reducing the

consumption of proteid food below the commonly accepted dietary

standards! We must admit, however, that there is a woeful lack of

agreement in these results, and it is difficult to prevent a shadow of

doubt from creeping over us as we try to depict for ourselves the way

in which a low proteid ration exerts its deleterious effect on dogs.

I do not believe that radical changes in diet, whether they involve

increase or decrease in total quantities, or in specific elements of

the diet, can be made suddenly without danger of some disturbance of

the gastro-intestinal tract or other parts of the economy, either

in dog or man. It is reasonable to believe also that a high proteid

feeder, like a dog, with his more limited dietary, will be far more

sensitive to great changes than omnivorous man with his wider range of

foodstuffs. Moreover, there is just as good ground for believing that

in any animal, excess of proteid is as dangerous as a low proteid diet.

Too great a disturbance in the nutritive balance, whether it involves

excess or reduction in the amount of a given foodstuff, is liable to be

attended with serious disturbance in any sensitive organism.

In illustration of these statements, we have some recent results

obtained by Watson and Hunter[71] upon the influence of diet on

growth and nutrition. These investigators find that young rats--two

and a half months old--when fed upon a diet composed exclusively of

horse-flesh, which is chiefly proteid matter with some fat, succumb

very quickly, for some reason. Of fourteen young rats fed on this meat

diet, six died on the third day. On the morning of this day, as the

authors state, “the rats appeared to be in their usual health, but

an hour after feeding one of them was lying on its side apparently

unconscious. In a few minutes others were affected. They appeared to be

paralyzed, they felt cold to the touch, exhibited symptoms of tetany,

and speedily became unconscious. Six succumbed within half-an-hour. Of

the remainder, some showed similar symptoms, although in less degree,

and they recovered when the diet was changed to bread and skim milk.”

After two days of the so-called normal diet, composed of bread and skim

milk, the remaining eight rats were again placed on an exclusive meat

diet. They appeared now to have acquired a certain degree of immunity,

for although they exhibited symptoms of deranged nutrition, these were

gradually recovered from and they gained in weight. At the end of the

eighth month, five of the animals were still alive and in apparent good

health, but their growth was permanently stunted. With an exclusive

diet of ox-flesh, young rats were much more liable to thrive, although

their growth was distinctly retarded.

[71] Chalmers Watson, M.D., and Andrew Hunter, M.B.: Observations

on Diet. The Influence of Diet on Growth and Nutrition. Journal of

Physiology, Vol. XXXIV, p. 112, 1906.

This difference in the behavior of the animals towards the two

forms of proteid food is to be attributed to the fact that ox-flesh

contains more fat than horse-flesh, and consequently the diet with

this form of meat was less exclusively proteid in character. Further,

there were some indications that horse-flesh is less digestible than

ox-flesh. Another fact, showing the far-reaching effect of a distinctly

unphysiological diet, is the marked influence of pure meat food on the

progeny. Thus, of 93 rats born of meat-fed parents only 19 were alive

at the end of two months, while of 97 young born of bread and milk-fed

rats, 82 were alive and in apparent health at the end of the same

period.

As illustrating how foods that have, superficially at least,

approximately the same chemical composition may react differently

in the animal body we have the observations of Watson on rats fed

with porridge, made by boiling oatmeal with water and skim milk,

as contrasted with a diet of bread and skim milk, the two diets

having essentially the same composition. Of fourteen young rats fed

exclusively on porridge, all, with the exception of two that were

withdrawn, succumbed within five months, while the bread and milk-fed

animals thrived as usual. Adult rats, however, can live for prolonged

periods and maintain their weight on a porridge diet. It is believed

that the difference in the behavior of young rats to these two closely

allied forms of diet, is due to a difference in the digestibility of

the food, the porridge being presumably less readily digested by the

young animals than bread. With the more fully developed digestive

powers of the adult animals, however, this difference in availability

practically disappears as a potent factor in their nutrition. Finally,

mention may be made of the fact that a pure rice diet, notably

deficient in proteid, arrests the growth of young rats and leads to a

fatal issue within three months, while adult rats placed on such a

diet lose weight rapidly and die in about the same time. All of these

facts bearing on the nutrition of animals quite remote from man have

significance as showing how any wide departure from a physiological

diet, for that particular species or type, may lead to very undesirable

results, and they warn us not to be too hasty in drawing far-reaching

conclusions and sweeping deductions from a few experiments with a given

species of animal.

Recurring now to the experiments made with dogs, there is certainly

suggested an element of danger in a low proteid diet, which, if the

experiments are taken at their face value and the conclusions derived

therefrom applied to man, needs careful consideration. Jägerroos

plainly was not inclined toward the belief that a low nitrogen intake

was the cause of the unfortunate results that attended his experiments.

Still, his animals did die from some cause, and thereby his position

was weakened. Munk and Rosenheim, on the other hand, from their

experiments were apparently convinced that a low proteid intake was

inimical to dogs, and it will be remembered Rosenheim concluded that

“a daily ration containing even 0.32 gram of nitrogen per kilogram of

body-weight, and with a fuel value of 110 calories per kilo, is not

sufficient to maintain the animal in a condition of health.” If this

is really true, there is some ground for the arguments advanced by

critical writers regarding the general subject of nitrogen requirements

of man. The evidence and the arguments, however, have always seemed to

the present writer frail and faulty; but recognizing the hold they have

taken on physiologists and the way they are usually applied to man, I

have attempted to test the matter experimentally under conditions which

would yield trustworthy and conclusive results.

The question how far results obtained with dogs can be applied safely

to man may be open to discussion, but we must first be sure of our

facts before arguments or conclusions of any kind are warranted. It is

to be remembered that dogs are as sensitive in many ways as man, and no

physiological experiment covering a long period of time can be carried

out with any hope of success unless there is due regard for proper

hygienic conditions, some degree of variety in diet, and reasonable

opportunities for fresh air and occasional exercise. I fancy that

even the most vigorous and hardy man, if confined for six consecutive

months in a room just large enough to furnish requisite air-space and

to permit of extending his body at full length, would find himself

at the end of such a period in a condition far from healthful, even

though there were perfect freedom of choice in diet. If, however, there

were added to the above conditions monotony in diet extending through

many months, there would be no occasion for surprise if the individual

lost appetite and strength, and showed signs of disturbance of the

gastro-intestinal tract.

It is doubtful if there is full appreciation of the possible effect

of monotony, in the ordinary dietary experiments on dogs. Man quickly

feels the effect; the sportsman camping in the woods by brook or lake

enjoys his first meal of speckled trout and has no thought of ever

becoming tired of such a delicacy; but as trout cooked in various ways

continue to be placed before him three times a day, and with perhaps

very little else, he soon passes into a frame of mind where salt pork

would be a luxury, and where he would prefer to go hungry rather than

eat the delicacy, if indeed he has appetite to eat anything. Is it

strange that dogs confined in cages barely large enough to permit of

their turning around, and fed day after day and month after month with

exactly the same amount of desiccated meat, fat, and rice, should show

signs and symptoms, if nothing worse, of disturbed nutrition? It is

necessary in experiments of this kind that the animals be confined

for given periods, at least, since otherwise it would be impossible

to determine the extent of nitrogen excretion and the rate of proteid

katabolism, etc. It is possible, however, to limit the time of close

confinement to, say, ten consecutive days, this to be followed by a

like period of comparative freedom, thus insuring opportunities for an

abundance of fresh air and exercise.

The experiments of which I wish to speak, and which had for their

object a study of the effect of low proteid diet on dogs, as types

of high proteid animals, were carried out at our laboratory in the

Sheffield Scientific School and were made possible by liberal grants

from the Carnegie Institution of Washington, thus providing means for

securing the requisite number of chemical assistants. The experiments

were conducted on a somewhat large scale, over twenty dogs being made

use of, while many of the experiments extended through a full year.

The results in their entirety are not yet ready for publication, but

I am able to present in a general way observations on six dogs, which

will serve as an ample illustration of what may be expected with high

proteid animals when living on a low proteid diet under healthful

conditions. All of the six dogs whose cases are here presented were fed

on a mixed diet, with some fresh meat each day; bread, cracker dust,

milk, lard, and rice being the other foods drawn upon to complete the

dietary. The animals were fed twice a day, each meal being accurately

weighed and of definite chemical composition. A large, light, and

airy room, kept scrupulously clean, and in the winter time properly

heated by steam, served as their main abiding place. In this room

were a suitable number of smaller compartments, the walls of which

were composed of open lattice work (of iron), so as not to interfere

with light or air, and yet adequate to keep the dogs apart. These

compartments were not cages in the ordinary sense, but were truly large

and roomy. The entire floor under the dogs was composed of metal, the

joints all soldered, the floor being sloped to a metal gutter in front

so that all the compartments could be flushed out each morning and kept

sweet and clean. In pleasant weather, immediately after their first

meal, the dogs were taken out of doors to a large enclosure near by,

where they were allowed perfect freedom until about four o’clock, when

they were taken in for their second meal (between four and five o’clock

in the afternoon). The outdoor enclosure was inaccessible to every one

except the holder of the key, and the dogs while there were wholly free

from annoyance. Once every month, during a period of ten consecutive

days, each dog was confined in the metabolism cage so as to admit of

the collection of all excreta, in order to make a determination of

the nitrogen balance. Practically, therefore, each dog was in close

confinement only one-third of the month, the remaining two-thirds

being spent in much more congenial surroundings. I have entered thus

fully into a description of the conditions prevailing, because I deem

them exceedingly important, and because therein undoubtedly lies the

explanation of the striking contrast between our results and those of

the earlier investigators of this subject.

In considering the outcome of our experiments, it may be wise to enter

into some detail concerning the first case to be presented. The animal

employed in this experiment was designated as No. 5, and weighed on

July 27, 1905, 17.2 kilograms; it was apparently full grown, but was

thin and had the appearance of being underfed. At first, it was given

daily 172 grams of meat, 124 grams of cracker dust, and 72 grams of

lard, the day’s ration containing 8.66 grams of nitrogen and having a

fuel value of 1389 calories.[72] These figures are equivalent to 80

calories, and 0.50 gram of nitrogen, per kilogram of body-weight. The

animal took kindly to the diet, but on August 3 it refused to eat and

seemed to have a little fever. The next day it was better, but for

the three following days its appetite was poor, and only a portion

of the daily food was eaten. Body-weight began to fall off, and was

soon at 15.5 kilograms. On the 7th of August, a dose of vermifuge

was given, after which the appetite returned and the animal appeared

in good spirits. From this time forward it seemed in perfect health,

with good appetite, and showed the usual vivacity and playfulness of

dog-kind. The diet as specified was continued unchanged until August

25, a balance experiment covering a period of ten days, from the 15th

to the 24th of August inclusive, being carried out, in which the

nitrogen of the intake was compared with the output for each day. From

the accompanying table, where are given the average values of all the

balance periods of the experiment, it is to be seen that during this

first period the animal was laying on or gaining an average of 2 grams

of nitrogen per day.

[72] The fuel value of the food was calculated from the data given

in Bulletin No. 28, U. S. Department of Agriculture. All figures for

nitrogen were obtained by exact chemical analysis.

SUBJECT No. 5. DAILY AVERAGES

+----------------+-------+-----------------------+-------------------------+------+

| | +------+-------+--------+---------+-------+-------+ |

| Date. |weight.|Total |gen per| Value | gen | gen | gen | gen |

+----------------+-------+------+-------+--------+---------+-------+-------+------+

|Aug. 15-Aug. 24 | 15.8 | 8.66 | 0.54 | 87.3 | 5.44 | 0.70 | 0.52 |+2.00 |

|Sept. 6-Sept. 15| 17.1 | 4.76 | 0.27 | 72.4 | 3.41 | 0.32 | 0.48 |+0.55 |

|Oct. 8-Oct. 17 | 17.6 | 4.76 | 0.27 | 71.8 | 3.54 | 0.54 | 0.49 |+0.19 |

|Nov. 22-Dec. 1 | 16.9 | 4.77 | 0.28 | 72.0 | 3.76 | 0.39 | 0.32 |+0.30 |

| 1906 | | | | | | | | |

|Jan. 2-Jan. 11 | 17.2 | 4.07 | 0.23 | 72.0 | 3.19 | 0.54 | 0.35 |-0.01 |

|Jan. 30-Feb. 8 | 18.0 | 4.07 | 0.23 | 69.0 | 2.87 | 0.54 | 0.62 |+0.04 |

|Feb. 27-Mar. 8 | 18.2 | 5.18 | 0.28 | 73.0 | 3.69 | 0.66 | 0.74 |+0.09 |

|Mar. 27-Apr. 5 | 18.3 | 5.23 | 0.28 | 73.0 | 3.66 | 0.84 | 0.48 |+0.25 |

|Apr. 24-May 3 | 19.1 | 5.22 | 0.27 | 68.0 | 3.76 | 0.38 | 0.48 |+0.60 |

|May 22-May 31 | 19.4 | 5.22 | 0.26 | 65.0 | 3.44 | 0.31 | 0.48 |+0.99 |

|June 17-June 26 | 20.0 | 5.24 | 0.26 | 67.0 | 3.50 | 0.71 | 0.48 |+0.55 |

+----------------+-------+------+-------+--------+---------+-------+-------+------+

[73] All through the balance periods the dogs were catheterized each

morning to insure complete collection of the twenty-four hours’ urine.

On August 25, a radical change was made in the diet, by reducing the

amount of meat to 70 grams daily, thereby lowering the intake of

nitrogen to 4.76 grams, or 0.27 gram per kilo of body-weight; the

cracker dust and lard being kept at essentially the same levels as

before. This diet was continued through the next balance period, the

dog in the meantime gaining in body-weight, and showing for the second

balance period an average gain by the body of half a gram of nitrogen

per day. The food was then altered by substituting bread for the

cracker dust, but so adjusted that the nitrogen and fuel values of the

day’s food remained practically unchanged. There was still, however, a

gain in body-weight and a slight gain in body nitrogen. At the close

of the third balance period, the diet was again altered, one-half of

the meat being replaced by milk, while cracker dust was substituted

for the bread. The morning meal consisted of 170 grams of milk, 86

grams of cracker dust, and 18 grams of lard, while the afternoon meal

was composed of 35 grams of meat, 63 grams of cracker, and 35 grams of

lard. The day’s ration, however, still contained 4.76 grams of nitrogen

and had a fuel value of 1249 calories. This diet was maintained until

November 20, when the animal was again placed on a daily ration of meat

(69 grams), bread (166 grams), and lard (80 grams), with a total fuel

value of 1228 calories and 4.77 grams of nitrogen. This was continued

until December 2, the dog still showing a plus nitrogen balance, but

with a little loss in body-weight. On December 2, the diet was again

changed by substituting milk for a portion of the meat, but the

nitrogen and fuel values were maintained at the same level as before.

After a week, December 9, the food was modified as follows: the morning

meal contained 170 grams of milk, 110 grams of rice, and 11 grams of

lard, while the afternoon meal was composed of 35 grams of meat, 81

grams of rice, and 30 grams of lard. The total nitrogen content of the

day’s ration was 4.07 grams, while the fuel value was 1255 calories. At

this time, the animal weighed 17.1 kilograms, consequently the intake

of nitrogen had been reduced to 0.23 gram per kilo of body-weight,

while the fuel value stood at 73 calories per kilogram. This diet was

continued until February 9, the balance period, between January 2 and

11, showing that the animal was in nitrogen equilibrium, in spite of

the material reduction in the intake of proteid, and that body-weight

was increasing. The next balance period, January 30 to February 8,

showed still further gain in weight with continuance of nitrogen

equilibrium. On February 9, the diet was changed by returning to 70

grams of meat, 158 grams of cracker dust, and 60 grams of lard, with a

daily intake of 0.28 gram of nitrogen per kilo of body-weight.

In this manner, the experiment was continued with frequent changes in

the character of the diet, but always maintaining essentially the same

values in nitrogen and calories as shown in the table, until June 27;

having extended through just eleven months, with the animal at the

close of the experiment still gaining in body-weight, with a steady

plus balance of nitrogen, and with every indication of good health and

strength. For ten months the animal lived with perfect comfort and in

good condition on an average daily intake of 0.26 gram of nitrogen

per kilogram of body-weight, and with an average fuel value of 70.3

calories per kilo. Further, it is to be observed that at no time

during the ten months did the daily intake of nitrogen rise above 0.28

gram per kilo, while during one month it fell to 0.23 gram per kilo.

Similarly, the fuel value of the daily food never exceeded 73 calories

per kilo, while at times it dropped as low as 67 and 65 calories per

kilo. That this diet was more than sufficient, both in nitrogen and

fuel value, is indicated by the steady increase in body-weight and by

the plus nitrogen balances observed in most of the periods throughout

the experiment. Indeed, with the comparatively low degree of muscular

activity which this animal was accustomed to, it would have been unwise

to have kept the subject much longer on a diet so rich as the above,

since there would have been danger of detriment to its health and good

condition. When these results are contrasted with the statements of

Munk and Rosenheim, the latter of whom found that even 0.32 gram of

nitrogen and 110 calories per kilo were insufficient to maintain dogs

in a condition of health, it is plain that for some reason our results

are quite at variance with their findings.

The accompanying photographs, taken on August 19, 1905, February 27,

April 24, and at the close of the experiment on June 27, 1906, show the

appearance of the animal at the respective dates, and indicate more

clearly than words can express the actual condition of the animal.

[Illustration: _Subject No. 5._ _August 19, 1905_]

[Illustration: _Subject No. 5._ _November 18, 1905_]

[Illustration: _Subject No. 5._ _April 24, 1906_]

[Illustration: _Subject No. 5._ _June 27, 1906_]

Turning now to a second subject, designated as dog No. 3, the

experiment with which lasted for nearly an entire year, the following

general statements may be made. The animal was a small black and white

fox terrier, weighing on July 6, 1905, 6.5 kilograms. It was a nervous,

affectionate little creature, far less phlegmatic than the animal just

described, always on the alert for a petting, and unceasingly active.

For these reasons, it seemingly required per kilogram of body-weight a

little more food than the preceding animal; a fact also in harmony with

the general law that small animals, per unit of body-weight, need more

food than larger ones. The diet made use of was of the same general

character as employed with the preceding animal, and was changed

from time to time to give requisite variety and to insure freedom from

too great monotony. The accompanying table, showing daily averages

during the twelve balance periods, gives all necessary information

regarding the outcome of the experiment.

SUBJECT No. 3. DAILY AVERAGES

+----------------+-------+-----------------------+-----------------------+------+

| | +------+-------+--------+-------+-------+-------+ |

| Date. |weight.|Total |gen per| Value | gen | gen | gen | gen |

+----------------+-------+------+-------+--------+-------+-------+-------+------+

|July 18-July 28 | 6.8 | 5.88 | 0.84 | 79.0 | 5.58 | 0.43 | 0.05 |-0.18 |

|Aug. 15-Aug. 24 | 7.1 | 3.44 | 0.49 | 77.4 | 3.35 | 0.17 | 0.13 |-0.21 |

|Sept. 6-Sept. 15| 6.9 | 2.11 | 0.30 | 80.0 | 1.93 | 0.21 | 0.07 |-0.10 |

|Oct. 8-Oct. 17 | 6.9 | 2.10 | 0.30 | 80.0 | 1.83 | 0.20 | 0.07 | 0 |

|Nov. 22-Dec. 1 | 6.0 | 1.83 | 0.31 | 80.0 | 1.48 | 0.21 | 0.11 |+0.03 |

| 1906 | | | | | | | | |

|Jan. 2-Jan. 11 | 5.6 | 1.63 | 0.29 | 81.0 | 1.54 | 0.17 | 0.08 |-0.16 |

|Jan. 30-Feb. 8 | 5.5 | 1.63 | 0.30 | 82.0 | 1.60 | 0.15 | 0.05 |-0.17 |

|Feb. 27-Mar. 8 | 5.5 | 1.78 | 0.32 | 84.0 | 1.66 | 0.17 | 0.05 |-0.10 |

|Mar. 27-Apr. 5 | 5.7 | 1.98 | 0.34 | 81.0 | 1.75 | 0.21 | 0.06 |-0.04 |

|Apr. 24-May 3 | 5.7 | 1.98 | 0.34 | 83.0 | 1.68 | 0.13 | 0.13 |+0.04 |

|May 22-May 31 | 5.8 | 1.98 | 0.34 | 80.0 | 1.77 | 0.13 | 0.11 |-0.03 |

|June 17-June 26 | 6.0 | 1.98 | 0.33 | 77.0 | 1.53 | 0.21 | 0.07 |+0.17 |

+----------------+-------+------+-------+--------+-------+-------+-------+------+

It will be observed that during the first three months the animal

showed a tendency to gain in weight slightly, recalling that its

initial weight on July 6 was 6.5 kilograms. Later, the weight fell

off a little, but in March it showed an upward movement, though very

gradual. With the amount of proteid food given, it is evident that

the animal needed about 80 calories per kilo to maintain a condition

of body-equilibrium. Nitrogen equilibrium was practically maintained

throughout the larger portion of the twelve months, but evidently the

animal required 0.31–0.33 gram of nitrogen per kilogram of body-weight.

Attention may be directed, in view of the results reported by Munk

regarding loss of the power of absorption and utilization of proteid

food, to the figures showing the average daily output of nitrogen

through the excrement. It is plain from the data presented, that this

animal was not suffering from any trouble of this order; indeed, the

utilization of proteid food throughout the entire experiment was

exceedingly complete, as shown by the relatively small loss of nitrogen

through the excrement, thus implying vigorous and unimpaired digestion,

together with thorough absorption of the products formed.

The accompanying photographs show the appearance of the animal on

August 19, 1905, November 18, 1905, April 3 and June 27, 1906, the

close of the experiment.

[Illustration: _Subject No. 3._ _August 19, 1905_]

[Illustration: _Subject No. 3._ _November 18, 1905_]

[Illustration: _Subject No. 3._ _April 24, 1906_]

[Illustration: _Subject No. 3._ _June 27, 1906_]

Passing now to the third subject, we have an experiment of somewhat

shorter duration, viz., of nine months, but sufficiently long to

afford ample opportunity for any deleterious effect to manifest

itself. The initial weight of the dog, No. 13, was 14.5 kilograms on

September 14. The lowest intake of nitrogen was 0.26 gram per kilo

of body-weight per day, while the fuel value of the daily food was

during one period reduced to 55 calories per kilo. A daily proteid

consumption equalling 0.30 gram of nitrogen per kilo, with a total

fuel value in the day’s food of 66–70 calories per kilo, was clearly

quite sufficient to maintain nitrogen equilibrium and body-weight;

indeed, toward the end of the experiment, the animal commenced to gain

in weight quite noticeably on the above diet, and was laying by fairly

large amounts of nitrogen daily. The accompanying table gives the

average daily nitrogen exchange, etc., of the nine balance periods,

while the photographs, taken on the dates indicated under each, show

the appearance of the animal at various times.

SUBJECT No. 13. DAILY AVERAGES

+---------------+-------+-----------------------+-----------------------+------+

| | +------+-------+--------+-------+-------+-------+ |

| Date. |weight.|Total |gen per| Value | gen | gen | gen | gen |

+---------------+-------+------+-------+--------+-------+-------+-------+------+

|Sept. 24-Oct. 3| 14.0 | 7.22 | 0.52 | 86.0 | 6.40 | 0.71 | 0.19 |-0.08 |

|Nov. 5-Nov. 14 | 13.0 | 4.78 | 0.35 | 80.0 | 4.29 | 0.37 | 0.25 |-0.13 |

|Dec. 19-Dec. 28| 13.4 | 3.70 | 0.27 | 72.0 | 2.86 | 0.49 | 0.13 |+0.22 |

| 1906 | | | | | | | | |

|Jan. 16-Jan. 25| 14.1 | 3.72 | 0.26 | 70.0 | 3.16 | 0.61 | 0.16 |-0.21 |

|Feb. 13-Feb. 22| 14.3 | 4.26 | 0.30 | 78.0 | 3.54 | 0.67 | 0.37 |-0.32 |

|Mar. 13-Mar. 22| 14.1 | 3.62 | 0.26 | 55.0 | 3.29 | 0.46 | 0.14 |-0.27 |

|Apr. 10-Apr. 19| 14.2 | 4.59 | 0.32 | 73.0 | 2.84 | 0.51 | 0.10 |+1.14 |

|May 8-May 17 | 14.2 | 4.59 | 0.32 | 71.0 | 3.56 | 0.48 | 0.18 |+0.37 |

|June 5-June 14 | 15.3 | 4.58 | 0.30 | 66.0 | 2.98 | 0.55 | 0.28 |+0.77 |

+---------------+-------+------+-------+--------+-------+-------+-------+------+

[Illustration: _Subject No. 13._ _January 2, 1906_]

[Illustration: _Subject No. 13._ _February 27, 1906_]

[Illustration: _Subject No. 13._ _April 24, 1906_]

[Illustration: _Subject No. 13._ _June 19, 1906_]

Results of the same general tenor with dogs No. 15 and No. 20 are seen

in the appended tables, while the accompanying photographs testify

clearly to the general good condition of the animals up to the end of

the experiments. In No. 20 particularly, the great gain in body-weight

is to be noted, even though the fuel value of the food was reduced as

low as 64 calories per kilo, with the nitrogen intake at 0.28 gram per

kilo daily. Plainly, the day’s food could have been diminished still

more, with perfect safety to both body and nitrogen equilibrium.

SUBJECT No. 15. DAILY AVERAGES

+---------------+-------+-----------------------+-----------------------+------+

| | +------+-------+--------+-------+-------+-------+ |

| Date. |weight.|Total |gen per| Value | gen | gen | gen | gen |

+---------------+-------+------+-------+--------+-------+-------+-------+------+

|Nov. 5-Nov. 14| 9.2 | 3.35 | 0.36 | 82.0 | 2.95 | 0.11 | 0.14 |+0.15 |

|Dec. 19-Dec. 28| 8.9 | 2.61 | 0.30 | 75.0 | 2.47 | 0.12 | 0.12 |-0.10 |

| 1906 | | | | | | | | |

|Jan. 16-Jan. 25| 8.7 | 2.60 | 0.30 | 79.9 | 2.15 | 0.21 | 0.16 |+0.08 |

|Feb. 13-Feb. 16| 8.5 | 2.61 | 0.30 | 82.0 | 2.37 | 0.20 | 0.15 |-0.11 |

|Mar. 13-Mar. 22| 8.7 | 2.82 | 0.32 | 80.0 | 2.68 | 0.17 | 0.19 |-0.22 |

|Apr. 10-Apr. 19| 9.0 | 2.80 | 0.31 | 82.0 | 2.14 | 0.26 | 0.09 |+0.31 |

|May 8-May 17| 9.5 | 2.83 | 0.30 | 75.0 | 2.26 | 0.30 | 0.12 |+0.15 |

|June 5-June 14| 10.2 | 2.81 | 0.27 | 70.0 | 2.26 | 0.28 | 0.24 |+0.03 |

+---------------+-------+------+-------+--------+-------+-------+-------+------+

[Illustration: _Subject No. 15._ _January 2, 1906_]

[Illustration: _Subject No. 15._ _February 27, 1906_]

[Illustration: _Subject No. 15._ _April 24, 1906_]

[Illustration: _Subject No. 15._ _June 19, 1906_]

SUBJECT No. 20. DAILY AVERAGES

+---------------+-------+-----------------------+-----------------------+------+

| | +------+-------+--------+-------+-------+-------+ |

| Date. |weight.|Total |gen per| Value | gen | gen | gen | gen |

+---------------+-------+------+-------+--------+-------+-------+-------+------+

|Dec. 6-Dec. 15 | 15.9 | 8.35 | 0.52 | 82.0 | 6.03 | 0.74 | 0.38 |+1.20 |

| 1906 | | | | | | | | |

|Jan. 16-Jan. 25| 16.4 | 4.47 | 0.27 | 73.0 | 3.61 | 0.55 | 0.15 |+0.16 |

|Feb. 13-Feb. 22| 17.2 | 4.45 | 0.25 | 72.0 | 3.92 | 0.36 | 0.13 |+0.04 |

|Mar. 13-Mar. 22| 17.4 | 5.00 | 0.28 | 72.0 | 5.49 | 0.33 | 0.10 |-0.92 |

|Apr. 10-Apr. 19| 18.4 | 5.60 | 0.30 | 69.0 | 4.88 | 0.52 | 0.18 |+0.02 |

|May 8-May 17 | 19.6 | 5.58 | 0.28 | 69.0 | 3.85 | 0.75 | 0.38 |+0.60 |

|June 5-June 14 | 19.7 | 5.59 | 0.28 | 64.0 | 4.69 | 0.45 | 0.40 |+0.05 |

+---------------+-------+------+-------+--------+-------+-------+-------+------+

[Illustration: _Subject No. 20._ _January 2, 1906_]

[Illustration: _Subject No. 20._ _February 27, 1906_]

[Illustration: _Subject No. 20._ _April 24, 1906_]

[Illustration: _Subject No. 20._ _June 19, 1906_]

The illustrations so far presented, with the general agreement in the

character of the results, might perhaps be interpreted as indicating

that there is no difficulty whatever in bringing a high proteid

consumer, like a dog, down to a low level of proteid consumption.

This, however, would be a false impression. Much depends upon the

character of the proteid food, at least where any attempt at rapid

change is made, for a certain modicum of meat or other animal food

seems a necessary part of the daily diet if health and strength are

to be maintained. A dog transferred suddenly from a daily ration in

which meat and milk are conspicuous elements to a diet in which these

are wholly wanting is very liable to show disturbing symptoms almost

immediately. One case may be cited in illustration of these statements.

On September 29, 1905, dog No. 17, weighing 18.2 kilos, was placed on

a daily diet composed of 70 grams of fresh meat, 442 grams of milk,

300 grams of bread, and 28 grams of lard. This ration contained 9.06

grams of nitrogen and had a fuel value of 1465 calories, or 0.5 gram

of nitrogen and 80 calories per kilogram of body-weight. On October

11, the animal weighed 18.6 kilograms and was in perfect condition. On

the 13th, the meat was reduced to 34 grams per day, but the milk was

increased in amount so as to maintain the same nitrogen intake and fuel

value as before. This diet was continued until November 3, a balance

experiment covering ten days from October 22 to the 31 inclusive,

showing that the animal was laying by a little nitrogen. On November

3, the diet was changed to milk, bread, and lard, the fuel value being

maintained at 80 calories per kilo daily, while the nitrogen intake

was reduced to 0.30 gram per kilo. On this diet, the animal seemed to

thrive perfectly, and at the end of two weeks showed a body-weight of

18.2 kilograms. November 19, the milk was withdrawn, the bread being

increased so as to keep the daily nitrogen intake and the fuel value

unchanged. The day’s food was now composed of bread and lard solely,

but, as just stated, the nitrogen and fuel values were unaltered. In

four days’ time, however, a change began to creep over the animal; the

appetite diminished, and there was apparent a condition of lassitude

and general weakness which deterred the animal from moving about as

usual.

During the next week the animal grew steadily worse, and would eat

only when coaxed with a little milk or with bread softened with milk,

the diet of bread and lard being invariably refused. There was marked

disturbance of the gastro-intestinal tract; bloody discharges were

frequent; the mucous membrane of the mouth was greatly inflamed and

very sore; body-weight fell off, and the animal was in a very enfeebled

condition. This continued until December 4, with every indication that

the animal would not long survive, but by feeding carefully with a

little milk and occasionally some meat, improvement finally manifested

itself, and by December 18 there was good appetite, provided bread was

not conspicuous in the food. Body-weight, which had fallen to 15.5

kilos, was being slowly regained, and on December 30 the animal was

again placed on a weighed diet, consisting of 70 grams of meat, 442

grams of milk, 210 grams of cracker dust, and 10 grams of lard. This

diet contained 8.26 grams of nitrogen and had a fuel value of 1330

calories, equivalent to 0.5 gram nitrogen and 80 calories per kilogram

of body-weight. On January 12, 1906, the weight of the animal was 16.7

kilos, while in general condition there was nothing to be desired. The

food was then modified by diminishing the amounts of meat and milk fed

daily by one-half, thus reducing the nitrogen intake to 0.35 gram per

kilo of body-weight, but maintaining the fuel value of the food at 80

calories per kilo. Under this régime, body-weight still increased,

and on January 27 was 17.5 kilograms. A balance period, shown in the

accompanying table, extending from January 30 to February 8, affords

ample evidence that the body was laying by nitrogen.

SUBJECT No. 17. DAILY AVERAGES

+---------------+-------+-----------------------+-----------------------+------+

| | +------+-------+--------+-------+-------+-------+ |

| Date. |weight.|Total |gen per| Value | gen | gen | gen | gen |

+---------------+-------+------+-------+--------+-------+-------+-------+------+

|Oct. 22-Oct. 31| 18.3 | 9.06 | 0.49 | 80.0 | 7.73 | 0.66 | 0.28 |+0.39 |

| 1906 | | | | | | | | |

|Jan. 30-Feb. 8 | 17.6 | 5.77 | 0.33 | 78.0 | 4.12 | 0.44 | 0.21 |+1.00 |

|Feb. 27-Mar. 8 | 17.9 | 5.31 | 0.30 | 72.0 | 4.59 | 0.59 | 0.37 |-0.24 |

|Mar. 27-Apr. 5 | 18.1 | 5.33 | 0.29 | 70.0 | 5.63 | 0.89 | 0.27 |-1.52 |

|Apr. 24-May 3 | 18.4 | 5.90 | 0.32 | 68.0 | 5.06 | 0.49 | 0.30 |+0.05 |

|May 22-May 31 | 18.6 | 5.90 | 0.31 | 67.0 | 5.25 | 0.53 | 0.43 |-0.31 |

|June 17-June 26| 19.9 | 5.89 | 0.29 | 70.0 | 4.29 | 0.39 | 0.28 |+0.93 |

+---------------+-------+------+-------+--------+-------+-------+-------+------+

In all of the subsequent months, a small amount of meat was a part of

the daily food, but as is seen from the table of balance periods, the

total nitrogen intake and the fuel value of the food were reduced to

even lower levels per kilogram of body-weight. Yet the animal gained

steadily, until at the latter part of June the weight was considerably

above that noted at the commencement of the experiment in the preceding

October. Further, the animal was in nitrogen equilibrium or even

gaining nitrogen, and in perfect condition of health and vigor, as

is indicated by the accompanying photographs taken at the different

periods stated. Especially to be emphasized is the fact that during the

last six months of the experiment, the daily intake of nitrogen and the

fuel value of the food were as low or even lower than in November, when

the daily diet was limited to bread and lard. The disastrous result

which showed itself at once on this latter diet, with all animal food

excluded, was not due to low proteid or to deficiency in fuel value,

but simply to the fact that the animal for some reason could not

adjust itself to a simple dietary of bread and fat, although there was

ample available nitrogen and fuel value for the body’s needs. Something

was lacking, which meat or milk could supply, and this something was

indispensable for the maintenance of the normal nutritional rhythm.

[Illustration: _Subject No. 17._ _January 2, 1906_]

[Illustration: _Subject No. 17._ _February 27, 1906_]

[Illustration: _Subject No. 17._ _April 24, 1906_]

[Illustration: _Subject No. 17._ _June 27, 1906_]

This is by no means an exceptional case, but we can cite many other

examples of like results where the animal when restricted to a purely

vegetable diet, such as bread, pea-soup, bean soup, etc., reinforced by

an animal fat, quickly passed from a condition of health into a state

of utter wretchedness, with serious gastro-intestinal disturbance.

The results are not to be attributed to the lower utilization of the

vegetable food, for the disastrous effect is too quickly manifest, and

further, often shows itself when the animal plainly has a large store

of available nutriment in its own tissues.

This experiment with dog No. 17 has been dwelt upon at some length,

because it illustrates a very important principle in the nutrition

of a high proteid and carnivorous animal. As before stated, it is

not a question of high or low proteid simply, but involves possibly

the more subtle question of the relative value of specific forms of

proteid food. It will be noted that this statement is made somewhat

guardedly, in harmony with the caution necessarily called for in view

of our lack of knowledge regarding the possible need of the animal’s

body for extraneous principles which only meat, milk, or other animal

products can supply. Inorganic salts, nitrogenous extractives, and

other substances without any appreciable fuel value, are quite likely

to be of primary importance in controlling and regulating the various

processes of the body, which combine to maintain the condition of

normal nutrition. With a diet restricted to one or two vegetable

products, it is quite conceivable that something may be lacking

which the system demands, though it cannot be measured in terms of

nitrogen or calories. It may be said that man thrives on a purely

vegetable diet, but while this is unquestionably true, it must be

remembered that man with his free choice of food has recourse, as a

rule, to a large variety of vegetable products from many sources,

and consequently there is great likelihood of his absorbing from

these varied products such supplementary matters as may be needed. On

this question, we are in a realm of doubt and uncertainty, but the

possibilities suggested must not be ignored, for they may contain a

germ of truth of the utmost importance. The fact remains, however, that

a dog when restricted to a purely vegetable dietary does not thrive; a

little animal food seems necessary to keep up health and strength, and

this suffices even though the daily nitrogen intake and fuel value of

the food are restricted to a level below that of the vegetable dietary.

With these facts before us, it is difficult to avoid the conclusion

that some significance may attach to the specific nature of the

proteid. Of course, we must not overlook the radical difference in

dietary habits of man and dog. Man as an omnivorous creature has for

generations been accustomed to partake largely of vegetable foods,

and as a result his digestive tract and his system as a whole has

become acclimated, as it were, to the nutritive effects of vegetable

matter. Dogs, on the other hand, are typical carnivores, and their

habits for generations have led in an opposite direction, so that their

gastro-intestinal tracts and their systems have become accustomed

to the effects of a diet in which animal food largely predominates.

Whether these deeply ingrained characteristics are responsible in

any large measure for the difference in behavior of man, on a purely

vegetable diet, and dogs is open to question. It would certainly not be

strange if such were the case, but as we look at the facts collected in

our study of this subject, it is somewhat impressive to note how well

dogs thrive on a relatively large amount of vegetable food, provided

there is a modicum of animal food added thereto. In other words,

these high proteid consumers are apparently quite able to utilize the

vegetable foods, but there is something lacking in such a dietary

which the body has great need of. Is it not quite possible, as already

suggested, that the specific nature of the proteid counts for something

in nutrition? The question cannot be answered definitely at present,

but there are certain facts slowly accumulating which make the question

a pertinent one in this connection.

Thus, it is becoming evident, as was pointed out in an earlier chapter,

that the many proteid substances occurring in the animal and vegetable

kingdoms are more or less unlike each other in their chemical make-up.

They yield different decomposition products, or the same products

in widely different proportion, when broken down by the action of

hydrolyzing agents; and when we recall that the digestive enzymes of

the body convert the proteids of the food into these same end-products,

it is plain that in the assimilation and utilization of the proteid

foodstuffs the body has to deal with these various chemical units.

Hence, an animal suddenly restricted to a dietary in which all of the

proteid is furnished by bread might be seriously incommoded, either by

the excess of certain amino-acids resulting therefrom, or by a lack

of certain other end-products to which its body is accustomed. As an

example, we may take the three typical proteids of the wheat kernel,

gliadin, glutenin, and leucosin, and note the very striking difference

in the proportion of certain of the decomposition products of each, as

reported by Osborne and Clapp.[74]

[74] See Osborne and Clapp: The Chemistry of the Protein Bodies of

the Wheat Kernel. American Journal of Physiology, vol. 17, p. 231.

+-----------------+-------------+-------------+-------------+

| | | | |

| | | | |

+-----------------+-------------+-------------+-------------+

| Leucin | 5.61 | 5.95 | 11.34 |

| Lysin | 0 | 1.92 | 2.75 |

| Arginin | 3.16 | 4.72 | 5.94 |

| Glutaminic acid | 37.33 | 23.42 | 6.73 |

| Ammonia | 5.11 | 4.01 | 1.41 |

| Aspartic acid | 0.58 | 0.91 | 3.35 |

| Tyrosin | 1.20 | 4.25 | 3.34 |

+-----------------+-------------+-------------+-------------+

It is obvious from these figures that the three proteids of the wheat

kernel are radically different from each other. Contrast, for example,

the content of glutaminic acid in gliadin with the amount in leucosin.

With such striking differences in chemical make-up, it is reasonable

to assume that corresponding differences in physiological action or

food values may exist. Further, “in respect to the amount of these

amino-acids, leucosin more nearly resembles the animal proteins than

the seed proteins thus far examined, and in this connection it is

interesting to note that leucosin occurs chiefly if not wholly in the

embryo of this seed and is probably one of its ‘tissue’ proteins, in

contrast to the ‘reserve’ proteins of the endosperm of which gliadin

and glutenin form the chief part” (Osborne and Clapp). In other words,

animal proteids, such as those of meat, are characterized like leucosin

by a small content of glutaminic acid and ammonia; while leucin, lysin,

aspartic acid, and arginin are relatively more abundant. Until we know

more on this subject, however, any broad generalization would be out

of place, but certainly there is justification for the supposition

that in these differences in chemical constitution are to be found

explanation of some of the peculiarities common to certain varieties of

proteid food. Wheat flour, aside from its starch, is composed mainly

of glutenin and gliadin with their large content of glutaminic acid.

Meat proteids, on the other hand, like leucosin, contain only a small

fraction of this acid, and, with the other differences indicated,

meat proteid and wheat proteid as food for dogs or other high proteid

consumers may reasonably be expected to have at the least very unequal

values. And if we go a step beyond this and suppose that in the

formation of true tissue proteid or the living protoplasm of the cell,

certain of these end-products of proteid decomposition are absolutely

indispensable, we can easily picture for ourselves a dearth of such

building stones in the long-continued use of a diet which lacks that

particular proteid from which the necessary building stones can be

split off in adequate number.

It has been said, notably by Munk, that in dogs fed for some time on

a low proteid diet there is a diminished power of absorption from the

intestinal tract, associated with weakened digestion. If it is true

that a lowered proteid intake results in a diminished utilization of

the ingested food, that efficiency in the digestion and absorption of

foodstuffs is impaired, it can only be interpreted as meaning that

some injurious influence has been exerted on the epithelial cells of

the intestine or the adjacent gland cells. We have, however, failed

to find any evidence of deleterious action in the dogs that we have

experimented with, where due regard was paid to maintaining a diet

suitable for the physiological needs of the body. In the experiments

that we have cited, both nitrogen intake and the fuel value of the food

per day were lower than in Munk’s experiments, but the utilization of

fat and proteid was not sensibly affected. The following tables give

the results with ten dogs (including the six dogs already described)

for lengths of time ranging from seven to twelve months, the periods

indicated being each of ten days’ duration and occurring once each

month. In the first table, the utilization of fat is shown, the

figures given being based on determinations of the amount of fat

contained in the excrement. Knowing the amount of fat in the daily

food and the amount which passed through the intestine, it is easy to

calculate the percentage of fat utilized.

UTILIZATION OF FAT IN PERCENTAGES.

+----------+-------------------------------------------------+

| | Dogs. |

| Periods. +----+----+----+----+----+----+----+----+----+----+

| | 1 | 2 | 3 | 4 | 5 | 12 | 13 | 15 | 17 | 20 |

+----------+----+----+----+----+----+----+----+----+----+----+

| 1 | 97 | 96 | 93 | 97 | 97 | 96 | 96 | 98 | 98 | 95 |

| 2 | 96 | 96 | 98 | 98 | 98 | 94 | 95 | 97 | 98 | 95 |

| 3 | 98 | 97 | 97 | 99 | 96 | 97 | 97 | 98 | 94 | 98 |

| 4 | 98 | 96 | 97 | 97 | 96 | 94 | 95 | 98 | 97 | 97 |

| 5 | 96 | .. | 94 | 98 | 97 | 95 | 95 | 98 | 97 | 96 |

| 6 | 97 | 98 | 94 | 98 | 97 | 96 | 94 | 97 | 96 | 97 |

| 7 | 97 | 98 | 98 | 97 | 96 | 93 | 95 | 97 | 98 | 96 |

| 8 | .. | .. | 98 | 96 | 96 | 96 | 93 | 97 | .. | .. |

| 9 | .. | .. | 98 | 97 | 98 | .. | 97 | 98 | .. | .. |

| 10 | .. | .. | 98 | 97 | 98 | .. | .. | .. | .. | .. |

| 11 | .. | .. | 97 | 92 | 97 | .. | .. | .. | .. | .. |

| 12 | .. | .. | 97 | 97 | .. | .. | .. | .. | .. | .. |

+----------+----+----+----+----+----+----+----+----+----+----+

It is perfectly plain from these results that there was no falling off

in the utilization of fat; the percentage amount digested and absorbed,

as in dogs 3 and 4, was just as large at the end of the twelve months’

experiment as at the beginning. Clearly, a so-called low nitrogen

intake with dogs does not lead to any loss of power in the utilization

of the fat of the food. This being so, it is equally clear that the

arguments based on Munk’s results in this direction, and applied to

man, are without adequate foundation.

UTILIZATION OF NITROGEN IN PERCENTAGES.

+----------+-------------------------------------------------+

| | Dogs. |

| Periods. +----+----+----+----+----+----+----+----+----+----+

| | 1 | 2 | 3 | 4 | 5 | 12 | 13 | 15 | 17 | 20 |

+----------+----+----+----+----+----+----+----+----+----+----+

| 1 | 95 | 91 | 92 | 94 | 91 | 91 | 90 | 93 | 92 | 91 |

| 2 | 92 | 94 | 94 | 95 | 93 | 90 | 92 | 96 | 92 | 87 |

| 3 | 91 | 92 | 90 | 91 | 88 | 89 | 86 | 95 | 89 | 91 |

| 4 | 90 | 85 | 90 | 92 | 91 | 82 | 83 | 91 | 83 | 93 |

| 5 | 90 | 82 | 88 | 92 | 86 | 85 | 84 | 96 | 91 | 90 |

| 6 | 86 | 87 | 89 | 83 | 86 | 89 | 87 | 94 | 91 | 86 |

| 7 | 87 | 87 | 90 | 83 | 87 | 83 | 88 | 90 | 93 | 91 |

| 8 | .. | .. | 90 | 83 | 84 | 81 | 89 | 89 | .. | .. |

| 9 | .. | .. | 89 | 87 | 92 | .. | 87 | 89 | .. | .. |

| 10 | .. | .. | 93 | 85 | 94 | .. | .. | .. | .. | .. |

| 11 | .. | .. | 93 | 81 | 86 | .. | .. | .. | .. | .. |

| 12 | .. | .. | 89 | 92 | .. | .. | .. | .. | .. | .. |

+----------+----+----+----+----+----+----+----+----+----+----+

The figures in the above table were obtained by determining the

amount of nitrogen in the dried excrement from the animals, _i. e._

the amount that passed through the intestine unchanged;[75] and

knowing the content of nitrogen in the daily food, the percentage of

unabsorbed nitrogen was then easily calculated, after which by simple

subtraction the percentage of utilized nitrogen was found. At first

glance, it would appear that as the experiments proceeded utilization

of nitrogen was less complete. In a sense, this was true, but it was

not connected with any impairment of the digestive or absorptive

powers of the intestine. It must be remembered that in the earlier

periods a larger proportion of the ingested nitrogen was in the form of

readily digestible meat, but as the latter was reduced in amount larger

proportions of vegetable food were introduced in order to maintain the

desired fuel value, and consequently the percentage of non-absorbable

nitrogen was increased. The well-known difference in the availability

of animal and vegetable proteid has already been referred to in other

connections; a difference due not so much to any inherent quality in

the digestibility of the two forms of proteid as to the presence of

cellulose and other material in the vegetable food which retards in

some measure the action of the digestive juices. To this cause must

be ascribed the slight falling off in the utilization of nitrogen

noticeable in most of the experiments. If, however, the figures are

compared with those usually obtained on a diet largely vegetable in

nature, it will be seen that the utilization of nitrogen by these dogs

was in no sense abnormal.

[75] There is an unavoidable error here, since the excrement contains

not only undigested food, but also contains some nitrogenous matter

derived from the secretions of the intestine, etc.

These experiments on the influence of a low proteid diet on dogs, as

a type of high proteid consumers, taken in their entirety, afford

convincing proof that such animals can live and thrive on amounts of

proteid and non-nitrogenous food far below the standards set by Munk

and Rosenheim. The deleterious results reported by these investigators

were not due to the effects of low proteid or to diminished consumption

of non-nitrogenous foods, but are to be ascribed mainly to non-hygienic

conditions, or to a lack of care and physiological good sense in the

prescription of a narrow dietary not suited to the habits and needs

of this class of animals. Further, it is obvious that the more or

less broad deductions so frequently drawn from the experiments of

Munk and Rosenheim, especially in their application to mankind, are

entirely unwarranted and without foundation in fact. Our experiments

offer satisfying proof that not only can dogs live on quantities

of proteid food per day smaller than these investigators deemed

necessary, and with a fuel value far below the standard adopted by

them; but, in addition, that these animals are quite able on such a

diet to gain in body-weight and to lay by nitrogen, thereby indicating

that even smaller quantities of food might suffice to meet their true

physiological requirements.

The results of these experiments with dogs, which we have recorded in

such detail, are in perfect harmony with the conclusions arrived at by

our experiments and observations with man, and serve to strengthen the

opinion, so many times expressed, that the dietary habits of mankind

and the dietary standards based thereon are not always in accord with

the true physiological requirements of the body. If these views are

correct, and the facts presented seemingly indicate that they are,

it is time for enlightened people to give heed to such suggestions,

that their lives may be ordered more nearly in accord with the best

interests of the body. Physiological economy in nutrition is not a

myth, but a reality full of promise for the welfare of the individual

and of the community in general. Ignorance on dietary matters should

give place to an intelligent comprehension of the body’s needs, and an

adequate understanding of how best to meet the legitimate demands of

the system for nourishment under given conditions of life. It is said

that more than half the earnings of the working people of this country

is spent for food. Here, we have suggested another form of economy as

worthy of consideration; less important perhaps than that which relates

to health and strength, but still calling for thoughtful attention. We

cannot afford to be ignorant of these things; we must have definite

knowledge of the actual facts, and these can only be obtained by

careful research and investigation.

As a prominent writer on nutrition has well said, “The health and

strength of all are intimately dependent upon their diet. Yet most

people understand very little about what their food contains, how it

nourishes them, whether they are economical or wasteful in buying and

preparing it for use, and whether or not the food they eat is rightly

fitted to the demands of their bodies. The result of this ignorance is

great waste in the purchase and use of food, loss of money, and injury

to health” (Atwater). We all recognize the general force and truth of

this statement, but there is a surprising lack of appreciation of the

full significance of what is involved thereby. If it is true that the

demands of the body for proteid food--which of all foods is the most

expensive--are fully met by an amount equal to one-half that ordinarily

consumed, and that health and strength are more satisfactorily

maintained thereby, it is easy to see how the acquisition of dietary

habits leading to consumption of food in harmony with physiological

needs will result in a fruitful twofold economy; viz., economy in

expenditure, and of still greater moment, economy in the activities of

the body by which food and its waste products are cared for.