successive generations, in a manner apparently demonstrative of
hereditary derivation. It is true that here we have a problem not
without complication. Certain circumstances, as poverty of living,
dampness of locality, want of fresh air in houses, etc., promote
scrofula in children. Now, are we sure that it is from its parents
that each child, exposed to these morbific surroundings, has obtained
its disposition to strumous disorders? or may it not be that every
time the diathesis is thus originated de novo? It is to be answered
that decisive evidence in favor of inheritance is present in a number
of cases where the affection occurs so early in infancy as to be
almost or quite congenital in its beginnings; and in other instances
where removal of the parents into improved localities, and with better
living altogether, has not prevented the manifestation of the same
tendency in their offspring for two or three generations. The inquiry
does not differ very greatly in its nature from that concerning cases
of enthetic diseases--_e.g._ cholera, yellow fever, typhoid fever; as
to which the {128} succession of cases may be such as to allow
hypothetical explanation, either by transmission from one individual
to another or by the subjection of all to a common local infection or
epidemic influence. But in both sorts of cases crucial instances may,
with care, be found which determine at least the general etiological
law for each malady.
Pulmonary phthisis has been always considered to be, in a marked
degree, a hereditary disease, until, latterly, the hypothesis of a
tubercular virus has threatened to displace old views about it. If,
however, we accept the classification of cases of pulmonary
consumption approved by several leading pathologists, in which a
position is provided for non-tubercular phthisis, we may at least
place hereditary vulnerability, or proclivity to consumption, in this
category, while awaiting the final decision of science upon the real
nature and origin of tubercle. My own conviction continues to be
positive, that tubercular phthisis is often transmitted by
inheritance, in the same sense as other diseases are generally
so--namely, by the bestowal upon offspring of a constitution
especially liable to the occurrence of the disorder at the time of
life when it is generally most apt to appear. The investigations of
Villemin, Cohnheim, Schüller, Koch, Baumgarten, and others have given
(1882) much prominence to the idea of the possibility of the
transplantation of tubercle from one human or animal body to another.
Koch's elaborate experiments especially are asserted to have shown the
existence of a bacillus tuberculosis, a true, minute vegetative
organism, which can be cultivated outside of the body, in a suitable
material, at a temperature like that of living blood, and which, when
inoculated, produces tubercular disease. The discussion of this
subject will occur on a later page as a part of the general topic of
the causation of enthetic diseases.
Rickets occupies a much less prominent place in the experience of
American practitioners than in that of some countries abroad, and it
is therefore less easy here to obtain materials for the study of its
etiology. Among those who have had large opportunities for its
observation, opinion is divided very much in the manner above referred
to. Thus, Wiltshire and Herring assert it to be certainly hereditary;
Jenner denies this altogether, while Aitken adopts the ground that
predisposing causes are derived from the parents or the nurse, which
are so capable of influencing the health of the child as to lead in
course of time to the establishment of the disease.
Goitre is manifestly a family disorder to a large extent in certain
regions, most familiarly in Alpine valleys in Switzerland. But this
local feature takes us back to the same kind of question: Is it the
transmission of a specially modified constitution from parents, or the
direct action of morbid local influences on the children themselves,
that produces bronchocele and its frequent attendant, cretinism?
Undoubtedly, goitre often occurs in children of healthy parents
brought from another locality into one where the disease is common;
and, per contra, goitrous subjects not infrequently recover from the
affection when removed for a length of time from the place where it
was developed in them. We are, apparently, at least safe in taking
here a position like that of Aitken concerning rickets: viz. that
predisposing causes are derived from parentage, whereby, more easily
than in those of different descent, certain influences will develop
goitre or cretinism, or both together.
{129} As to leprosy, there seems no more room for doubt that it is
often--nay, generally--hereditary. The obscurity attending its
history, however (more than one cutaneous affection having been from
time to time classed under the same name), will justify our referring
the reader for the particular discussion of its etiology to another
part of this work. (See DISEASES OF THE CUTANEOUS SYSTEM.)
Hæmophilia is clearly hereditary in certain families. Immermann
asserts it to be even a race-liability in the Jews. "Bleeders" upon
occasion of very small wounds of the skin, gums, etc. have been known
in several successive generations, including (Börner; Kehrer) women at
the time of parturition, who then are apt to have dangerous
hemorrhages.
Cancer presents as unmistakable examples of inheritance as any other
disease. Paget asserts this to be traceable in one case out of three;
Sibley, in one of nine; and Bryant, one of ten cases. De Morgan and
others have shown the same thing to be true of non-malignant morbid
growths. But, as Paget has remarked, when other local disease or
deformity is inherited, it usually involves in the offspring the same
tissue, often the same part of the body, as in the parent, but the
transmitted cancerous tendency may show itself anywhere: "Cancer of
the breast in the parent is marked as cancer of the lip in the
offspring. The cancer of the cheek in the parent becomes cancer of the
bone in the child. There is in these cases absolutely no relation at
all of place or texture."
Cataract is believed by good authorities to be promoted by hereditary
tendency. It is of the nature of a degeneration. Possibly, in a
greatly-prolonged decay of all the organs with age, all eyes tend to
become cataractous from structural alteration of the crystalline lens.
Under observation a quite different rate of degenerative change takes
place among the organs of the body in different individuals and
families. Thus, the lens becomes opaque in some at an age when the
hearing continues good and the muscles retain considerable vigor,
while in members of other families the eyes remain in a sound
condition at a time when other organs and powers have failed.
Congenital cataract appears to be altogether independent of any
proclivity transmitted from parents in the nature of an inheritance.
Affections of the nervous system very often show hereditary descent.
Neuralgia prevails strongly in certain families. Particularly, that
form of cephalalgia called sick headache is apt to appear, in the
periodical form, through several generations. Apoplexy and paralysis
are prone to occur at nearly the same time of life under the
transmission of like constitutions by parentage. Still more often this
has been observed of epilepsy and hysteria, and, most of all the
neuroses, in insanity. Monomania and melancholia have been in a great
number of instances traced to generative succession--sometimes,
especially suicidal monomania, through four or five generations.
Predisposition to intemperance, methomania, is also a terrible
inheritance in some families. Although the production of this malady
requires the provocative of indulgence in the use of alcohol for its
development, yet the facility with which this result occurs under the
same circumstances in different families is too marked to leave room
for doubt of its hereditary nature.
Less certainly, but with much probability, we may assign parental
endowment as one of the factors in the causation of organic disease of
{130} the heart, arteries, liver, and kidneys, as well as of angina
pectoris, asthma, croup, dyspepsia, and hemorrhoids.
Is a special proclivity to any of the group of enthetic febrile
diseases ever inherited? Dr. George B. Wood believed this to be the
case with enteric or typhoid fever. Few others have shared this
opinion, but it is not impossible that it has a basis of truth.
Reference has been made already to the difference between periodical
malarial fevers (intermittent, etc.) and yellow fever, in that an
attack of the latter does, and one of the former does not, protect the
individual, usually, from liability to the disease on exposure to its
cause. Does this protection extend to offspring of parents who have
been "acclimatized" to yellow fever? Facts on this point are not easy
to obtain. While, however, there appears to be no proof that a single
generation can ever suffice to outgrow (so to speak) liability to this
disease, it is well known that creoles in Louisiana and the West
Indies are less susceptible to it than recent white residents, and
that the negroes are much less so, as a race, than the whites.
Furthermore, negroes whose ancestors have long been domesticated in
our Southern States appear to re-acquire susceptibility to yellow
fever in a degree more nearly like that of white people than is
observed in natives of Western Africa imported within one or two
generations.
As to autumnal malarial fevers (remittent, intermittent), the black
race exhibits a sort of race-acclimatization, giving negroes, both in
Africa and in America, a much less degree of liability than is common
to all races of European descent.
How far any similar modification may occur in the course of
generations in regard to susceptibility to small-pox and allied
diseases remains at present a matter of speculation. Some authors
insist that there must be at least a kind of natural selection,
according to which a great epidemic of variola, destroying the lives
of many of those most predisposed to suffer from it, will leave the
remaining population less likely to be attacked by it. The endeavor
has even been made to explain away in this manner much of the
diminution of mortality from small-pox commonly credited to
vaccination. But the statistics of the ravages of variola in different
countries before and after the introduction of vaccination show that,
while we cannot deny that some alternation (of generations
respectively more and less susceptible) may occur, no such law can
compare in influence with that of vaccination in the protection of
individuals subjected to it. Indeed, the argument may be inverted;
thus: if in the days before Jenner small-pox itself weeded out the
persons most liable to it, or in some way prepared a partial family-
or race-protection, such a protection ought to be gradually conferred
upon a whole population through universal and persistent vaccination
carried on for several generations.
Is it possible for one hereditary constitution or diathesis to become,
in transmission, not only modified, but transmuted, into another? Some
of the older pathologists imagined this to be the case with syphilis,
to whose past influence upon parents and ancestors they traced the
origin of scrofula. But no sufficient ground for such a pathogeny can
be ascertained. All that appears to be left after scrutiny of the
facts is, that syphilis is a depressing and perverting agency, and so
may join with {131} other depressing causes in preparing the way for
the engendering of scrofulosis.
A few points still remain to be briefly mentioned in connection with
the hereditary conveyance of proclivity to disease. One or several
members of a family will often pass through life without any
manifestation of such transmission, while others, their brothers or
sisters, give marked evidence of it. Sometimes a whole generation may
be passed over, and yet the predisposition may be abundantly shown in
that next following. This is closely similar to atavism, as it is
called in zoology and general biology, according to which traits
occurring under admixture or variation of animal or vegetable stocks
may be absent in the immediate offspring of a couple, but reappear in
their next succeeding descendants, or even a still later reversion may
take place. Such instances are not rare, and they need to be
considered in the proper study of the influence of parentage,
intermarriage, etc. upon health and disease.
A practical question of much importance (belonging, however, rather to
sanitary than to medical science) is, how far confirmation or
modification of hereditary proclivities may occur through the effect
of the conditions of marriage upon offspring. Consanguineous marriages
have been, time out of mind, held to be very objectionable. The
question has been much discussed whether the ground of sanitary
objection is properly against such marriages as per se injurious to
offspring, or whether the bad effect consists merely in reduplicating
and intensifying family constitutional taints. It would not be in
place here to go into this controversy. My own conclusion is, that a
natural law of sexual polarity or affinity exists, according to which,
in all the higher organisms, reproduction is most normal and gives the
best results when a considerable genetic difference (within the limits
of species) exists between parents. While, however, this is probable,
but difficult to demonstrate, it appears to be certain that when a
father and mother both possess morbid constitutional predispositions
(say, to phthisis, insanity, or gout), their children will be at least
twice as likely to suffer from the same as if only one parent were so
endowed. Whether or not, then, the marriage of two perfectly healthy
first-cousins may be expected (as several statisticians aver to have
been shown) to be attended by defects of health in their progeny, the
union of such relations when their common progenitors were in marked
degree consumptive, or scrofulous, or liable to insanity, epilepsy,
etc., has attached to it so unfavorable a prognosis for offspring as
to be rightly forbidden. Moreover, so few families possess an
absolutely faultless health-record that the chances of increasing
existing morbid traits by intermarriages are quite sufficient to
justify the commonly held objection against them.
We must allude very briefly to the influence of conditions affecting
conception and gestation upon the health of offspring. Intemperance in
parents has, in many instances, been known to promote convulsions,
infantile or epileptic, and other cerebral or nervous disorders in
children, besides a general feebleness of constitution. Even
intoxication at the time of procreation has been asserted to mark a
similar difference between one child and another of the same parents.
All are familiar with the (no doubt often quite imaginary) accounts of
the effect on infants in utero of powerful sensory or mental
impressions upon the mother during gestation. Abortion has,
unquestionably, been {132} often produced by violent nervous shocks.
Without deciding the question whether "monsters" are ever developed in
correspondence with particular experiences of the mother, we may hold
it to be clear that all depressing and disturbing agencies may
interfere with the process of nutrition of the foetus, and thus
develop mental anomalies, and that constitutional impairments may thus
be greatly promoted.
All inherited predispositions, it is important to remember, are
aggravated, and each proclivity changed to actuality, by those
influences which in individuals tend to like effects upon health. Such
become exciting causes of various diseases. If these be constantly
avoided, and all the surroundings and the mode of life of the
individual be maintained in a manner most favorable to health, the
hereditary tendency may remain inert through a long lifetime. Every
physician must have seen this in scores of instances. The application
of the principle through special precepts belongs to personal hygiene.
But no physician can rightly ignore the study of this subject, or omit
the utilization of his acquaintance with it by preventive advice to
members of the families under his professional care.
Our last remark in connection with pre-natal causation must be upon
the effects of circumstances and modes of living on masses of men,
especially in large cities and populous countries. Something has been
said already of race-acclimatization by which there may be acquired a
lessened susceptibility to certain endemic fevers.[2] Almost a reverse
action is exhibited in the gradual lowering of vital energy under what
has been called the "great-town system." While those having all the
comforts of life and avoiding excesses may manifest but little of this
deterioration, it is very observable in that mass of men, women, and
children who become the subjects of medical charities. Closeness and
uncleanliness of living, with more or less exposure to dampness and
extremes either of heat or cold, with intemperance and syphilis, are
the main causes of this general constitutional impairment. So
important is it that it should never be forgotten, not only in our
estimate of the causation of diseases, but in our anticipation of
their results, and also in our adaptation of measures of treatment,
medical and surgical, to different classes of patients. All that it is
allowable here to suggest in this regard may be summed up (although
very imperfectly) in the word hospitalism.
[Footnote 2: It is important (but not before remarked in this article)
that cholera does not appear to allow of any such diminution of
liability to it among the natives of the country in which it is
endemic.]
Conditional causation has been, to a certain extent, included under
what has been above said, as it is the action, in part at least, of
surrounding conditions, that establishes a family- or race-proclivity
and inheritance. But we must say something more about the direct
action of conditions upon individuals.
Man, although organized with great delicacy of structure, is capable,
by the use of his intelligence, of adapting himself to a wider variety
of external conditions than any other animal. He is the only truly
cosmopolitan being on the earth. From the remote Arctic regions to the
hottest tropical climates there are tribes whose ancestors have dwelt
for centuries in the same localities. Not that no unfavorable
influence attends these extremes. The Esquimaux are stunted, the
Southern Hindoo and {133} Central African are enfeebled and
degenerate, partly from climate. But with man's numerous protective
devices, great cold and great heat only exceptionally affect
individual health. Freezing to death follows unusual exposures; the
loss of an extremity by sphacelus from congelation is more often met
with; heat-stroke also is tolerably frequent; and the influence of
heat in producing cholera infantum in some large cities is very
important; but much the most common kind of conditional morbid
causation is produced either by sudden changes of temperature or by
diversity of exposure of different parts of the body. These are the
two usual modes of "taking cold." When dampness accompanies a
relatively low temperature, such an effect is much more apt to follow
than in a cold dry atmosphere.
Actual cold-stroke, the analogue of heat-stroke, may sometimes happen.
I once saw such a case in a previously healthy boy twelve years of
age, who, after standing for an hour in his night-shirt on a cold
winter night, became almost immediately ill, fell into a comatose
state, and died in about thirty-six hours.
A simple rationale may be discerned for the phenomena of catching
cold. When, for example, a draught of air blows for a time upon the
back of a person at rest (especially one who has just before used
active exertion), the local refrigerant impression induces
constriction of the superficial blood-vessels. Hence follow two
effects: one, the repulsion of blood in undue amount toward interior
organs; the other, diminution, perhaps arrest, of excretion from the
skin of the exposed portion of the body, and consequent retention of
some effete material, promoting esotoxæmia.[3] If, then, there be in
the body any weak organ--that is, one whose circulation is partially
impeded or whose nutritive and functional activity is low--it suffers
first and most from the impulsion of blood from the surface.
Congestion, irritation, and inflammation may follow, and we have an
attack of pneumonia, pleurisy, bronchitis, or some phlegmasia.
[Footnote 3: That is, blood-poisoning, originating within the body
itself; exotoxæmia being that which is enthetic--_i.e._ resulting from
a poison derived from without.]
Excessive heat with dryness, as under the blasts of the Simoon or the
Harmattan of Arabia or Northern Africa (apart from insolation,
sunstroke, or heat-stroke), may sometimes parch the body even to a
fatal degree. Much more common is the combination of high temperature
with humidity. This has a relaxing effect, promoting indolence of
temperament and predisposing to disorders of a catarrhal nature,
especially of the digestive organs, such as were called fluxes by the
older writers.
Cold climates are well known to present the greatest number of cases
of acute and chronic affections of organs of the respiratory system;
warm and hot climates, those of the stomach, liver, spleen, and
bowels. But we must recollect what various complications belong to
climate. Two important factors, especially, must be kept in view in
comparing the causation of diseases in colder and warmer
countries--namely, the difference in the articles of food partaken of
in each, and the external sources of enthetic disorders; _e.g._
endemic and epidemic fevers, etc.
With humidity must be considered variations in atmospheric pressure.
Physicists have long known that while watery vapor, by itself, is
heavier than air which is perfectly dry, moist air is lighter than air
containing {134} little or no moisture. Hence the barometer falls as
the quantity of atmospheric moisture approaches saturation. Other
causes, however, also affect barometric pressure. With the same degree
of humidity, cold air is denser and heavier than warm air, and by its
contraction lowering the "column" of atmosphere--the temperature of
which is reduced--a flow toward the upper part of the column increases
the actual mass of air pressing upon a particular place. Elevation of
a locality above the general level of the earth reduces atmospheric
pressure, sensibly as well as measurably. So "the difficult air of the
iced mountain-top" has become proverbial.
These variations are familiar, though all their effects upon human
health have been by no means, as yet, fully studied. Most difficult to
determine and analyze are the influences of changes of pressure,
chiefly hygrometric, upon the course of diseases and upon the result
of severe surgical operations. Among the few important series of
observations bearing on this topic have been those of Dr. S. Weir
Mitchell on neuralgia,[4] and Dr. Addinell Hewson on the prognosis of
major operations,[5] in connection with the state of the weather. The
former ascertained a marked relation between the approach of a wave of
low barometric pressure and attacks of irregularly periodic neuralgia;
the latter proved, by the statistics of the Pennsylvania Hospital for
a number of years, that the most favorable time for amputations or
other capital operations is when the barometer is high, or at least on
the ascent.
[Footnote 4: _American Journal of Medical Sciences_, April, 1877, p.
305.]
[Footnote 5: _Pennsylvania Hospital Reports_, 1868.]
Electrical atmospheric states and vicissitudes have, quite probably, a
practical consequence beyond what is usually ascribed to them in
connection with health and disease. But their effects are so difficult
to disentangle from those of other meteorological causes that we must
be content at present without attempting their exact specification.
The same observation may be made with reference to ozone.