already been considered. It may be added that meteorological
conditions have been supposed to favor the prevalence of the disease
among cows. More precise observations are needed to enable us to
determine whether or not there is any truth in this supposition. It
has been said that the affection is most apt to prevail during warm
and moist seasons. This is contrary to what we might have imagined, as
warmth and moisture are quite destructive of the vaccinal virus. Under
ordinary circumstances, however, the contagium often proves
wonderfully tenacious of life, and the disease, once introduced among
a herd of cows, is prone to linger for months, or even years,
attacking animals recently added to the stock and young cows during
their first lactation. As has already been stated, age, sex, and
parturition can be regarded as etiological factors only in so far as
they favor the occurrence of accidental inoculation. In the human
subject vaccinia occurs generally as the result of intentional
inoculation, as will be more fully referred to when we come to the
consideration of vaccination. Insusceptibility is occasionally met
with, both in the cow and in man, but it is very rare. Perhaps it may
be explained in some instances by the subject having really had the
disease, or indeed small-pox, either before or after birth, in so mild
a form as not to have left the characteristic marks. Certain it is
that the lesion does not always leave a permanent scar, especially in
the cow.
GENERAL COURSE OF THE DISEASE.--This is best studied in cases that
have followed intentional inoculation, for here we know the {459}
chronological sequence of events. Depending somewhat upon the method
of inoculation, and perhaps also to some extent upon the state of the
skin at the site of the inoculation, or even upon a systemic condition
(since some vaccinators hail it as a harbinger of success), at the
time of the operation a ring-like erythema may be seen surrounding the
inoculation. This is exceedingly evanescent, being doubtless due to
vaso-motor action, and is not often witnessed.
Ordinarily, no effect whatever is observed until after the lapse of
two or three days, when a red papule is formed. This papule increases
in superficial area, but not in height, and gradually loses its
redness. It assumes a circular form, or, in the case of a compound
pock (for that is the proper name for the lesion), a configuration
representing segments of several circles, and as it increases in area
it becomes more and more raised at the border (the bourrelet of French
writers), while the central portion, which also increases in size pari
passu with the peripheral annular vesicle, does not become more
elevated, but remains depressed, giving the pock as a whole the
peculiar shape termed umbilication. Up to the eighth or tenth day,
inclusive, the marginal elevation contains a limpid fluid termed
lymph, and consequently presents a pearl-like lustre. At this period a
rather sudden increase takes place in the corpuscular elements
contained in the lymph, causing that liquid to become thick and
opaque, so that the elevated margin of the pock, which before had
shown the pearl-like lustre alluded to, now comes to look as if made
of tallow.
At the same time what is known as the areola forms around the pock,
and constitutional symptoms show themselves. The areola is a
circumscribed redness of the skin, perfectly circular in form and of
five or six times the diameter of the pock itself. It is sharply
defined and of a vivid red hue. Usually it is a mere hyperæmia of the
skin, but in some instances, especially where the process of
pock-formation is decidedly pronounced, a few papillary elevations are
to be seen in the immediate neighborhood of the pock, and at that
situation there may also be some lividity. After a few hours'
persistence in the form of a disc the areola begins to disappear, the
redness fading first at the central portion, so that in its declining
stage it assumes the shape of a ring which constantly grows narrower
and narrower at the expense of its inner portion, and finally
disappears altogether. In the cow the areola is only a faint line
immediately around the pock.
Constitutional symptoms are invariably present in cases that follow
the regular course. The temperature rises one or two degrees
Fahrenheit, the appetite becomes impaired, and sleep is somewhat
disturbed. In many cases, mostly those of secondary inoculation, the
symptoms are more severe; the fever runs higher, and may be
accompanied with transient delirium; nausea is experienced, perhaps
with actual vomiting; and severe pain is felt in the head and along
the spine, the latter being most marked in the cervical region. These
symptoms usually last but a few hours, and they are apt to be
accompanied by a modification of the areola whereby it loses its
disc-like outline and becomes diffused irregularly, especially, if, as
is usual, the inoculation has been done on the arm, in a downward
direction toward the elbow.
Along with these phenomena intense itching is often felt at the
situation of the pock, being an aggravation of the pruritus that in a
mild {460} form accompanies the greater part of the whole course of
the lesion. Supposing the arm to have been inoculated, the lymphatic
glands of the axilla now become swollen and tender, but their
suppuration is unusual, and is to be regarded as a complication.
To go back to the pock: some time before the contents of the marginal
elevation become opaque the central portion is converted into a crust
of a brownish color, and finally, from the tenth to the fifteenth day,
the bourrelet itself, having ceased to increase in size, takes part in
the process of incrustation, the completed crust representing the form
of the pock, having a circular ridge at the border, at which part its
color is not so deep as at the centre. The crust usually falls off
between the fifteenth and the thirty-fifth day. It is hard,
translucent, and of a prune-juice color; thick at the centre and thin
at the periphery; smooth on its attached surface and somewhat wrinkled
on its outer aspect; surmounted at the centre by the epidermal débris
produced by the operation of inoculation, mingled perhaps with more or
less dried blood.
After the crust falls off a reddened surface is left of a cicatricial
nature, usually somewhat depressed below the level of the surrounding
skin, and frequently showing lesser pits, which latter appearance is
termed foveolation. Instead of these pits, radiated striæ are
frequently left. Gradually the scar loses its red color, and, like
other scars, finally becomes paler than the surrounding skin. It is
usually permanent.
IRREGULARITIES IN THE COURSE OF THE DISEASE.--Ever since cow-pox first
became the subject of medical study deviations from its typical course
have been noticed, and have been the theme of a good deal of
speculation. The older writers, indeed, bestowed no little attention
upon what they considered to be not irregular forms of vaccinia, but
distinct affections with which it was liable to be confounded. Their
descriptions of these diseases, which they termed spurious cow-pox,
are, however, so vague as to possess but little more than an
historical interest. In regard to affections met with casually in the
cow, we can often determine their nature only by test-inoculations,
and even that criterion is not always thoroughly convincing; for, on
one account or another, we may fail in the attempt to propagate true
cow-pox, and on the other hand, if we admit that there is a radical
difference between cow-pox and small-pox, it is manifest, bearing in
mind the errors into which experienced investigators have fallen, that
we may propagate small-pox through a long series of experiments
without once suspecting it to be anything but cow-pox. We may,
nevertheless, always determine, provided we succeed at all, whether we
are dealing with a disease that protects against vaccinal and
variolous inoculation.
In the human subject we seldom meet with affections that counterfeit
vaccinia, although, if we take only the lesion into consideration,
there are certain contagious forms of herpes that may give rise to
doubt, and possibly the same may be true of impetigo contagiosa.
Turning, then, to the irregularities properly so called, we have first
to consider the absence of constitutional infection. This must not be
confounded with the mere lack of obvious constitutional symptoms; what
is meant by the expression is, that in certain instances the local
lesion may appear typical, and yet no such impression be made upon the
system as to render it proof against subsequent inoculation. Early in
the {461} century the possibility of this lack of systemic infection
was insisted upon by Mr. Bryce of Edinburgh, who invoked it as an
explanation of the occasional failure of vaccinia to protect against
small-pox. The practical question was, how to decide, in a given
instance, whether general infection had or had not taken place. In the
opinion of many observers--and that notion has cropped out every now
and then up to the present day--absence of the areola furnished at
least presumptive evidence that the constitution had eluded infection.
But, whatever may be held theoretically, it must be conceded either
that the general system very rarely fails to feel the impress of the
disease, or else that the criterion is fallacious. For in an
experience of seventeen years the present writer has not known of a
single instance in which a vaccinal lesion that pursued a regular
course in other respects has failed to be accompanied by the areola.
And certainly Mr. Bryce himself must have attached little if any
importance to it, for he took great pains to establish a means of
determining the presence or absence of constitutional infection--the
so-called Bryce's test. This consists in repeating the inoculation at
a certain period in the evolution of the disease, the theory being
that systemic infection does not take place at once, but only after
the lapse of a number of days from the time of the inoculation. Up to
that time a repetition of the inoculation is possible, and, if
systemic infection results from the first one, both lesions will
mature at the same time, the second one following an accelerated
course, reaching its acme rapidly, although dwarfed in size. If, on
the other hand, the first inoculation failed to infect the
constitution, the second one will pursue its course in the usual
manner. Moreover, at a certain time, generally about the fifth day, a
repetition of the inoculation will fail altogether if the original
insertion has really infected the system. The present writer can
testify that Mr. Bryce's statements are correct; he has applied the
test in many cases, but in no instance has he been led to the
conclusion that constitutional infection had failed to take place. He
is inclined to think, therefore, that such failure is exceedingly
rare.
Passing over the multiplicity of irregularities in the lesion that
were described by the older observers, it seems that there are a few
that are of practical importance. In the first place, there is a
variety of pock to which it is not easy to give a definite name, but
which is characterized by a lack of decided elevation above the
surrounding skin (a deficiency for which it makes up in superficial
area), by the early formation of a thin, flimsy, straw-colored crust,
and by the utter failure of the characteristic firm brown crust of the
typical variety to become developed. This form of irregular pock has
not been seen by the writer of late years, but before animal
vaccination came into general use he met with it frequently, mostly in
cachectic children. Notwithstanding its sprawly, unsatisfactory
appearance, it is undoubtedly genuine, for the typical lesion may be
produced by inoculation with its contents.
Another irregularity of the pock is what is familiarly termed the
raspberry excrescence. A red elevation forms at the seat of
inoculation, and at first promises to follow the typical course,
although it may be tardy in making it appearance; but it never
advances to full development. It becomes indolent, and may last for
several weeks, or even months, in the form of a hard, flat nodule of a
bright-red color, not unlike a small {462} nævus. In many instances it
has a succulent look, but no lymph can be obtained on puncturing it.
No areola appears at any time, and finally the lesion slowly
disappears, leaving no trace of its existence. It is probably an
abortive form of pock, in which only the papillary layer of the skin
takes part, without any exudation into the epidermis. It is seldom, if
ever, protective against small-pox, for it constitutes no bar to a
subsequent vaccination. This irregular pock has been observed from
time to time ever since the early days of vaccination, but for the
past six years it has been seen more frequently in New York than for
many years before. Now, however, it seems to be growing less common.
The writer is not aware of any satisfactory explanation of its
occurrence. It is seen in all sorts of subjects, and seems to follow
the use of one variety of virus as much as the employment of any
other.
What has been termed generalized vaccinia is another form of
irregularity. The expression is a vague one, covering as it does not
only the very rare cases of true eruptive vaccinia, in which a general
eruption of pocks takes place as a consequence of constitutional
infection, playing the part of an exanthem, but in addition those
instances, not very uncommon, in which pocks are formed here and there
on the body, probably as the result of the accidental transfer of the
virus from the pock by scratching. Under such favorable
conditions--the immediate transfer of lymph from a pock in which the
specific evolution is going on vigorously--the slightest penetration
of the epidermis with the nails is enough to secure self-inoculation.
In view of this facility with which it may be effected, we should be
very careful not to jump hastily to the conclusion that in any given
case of generalized vaccinia the supplementary pocks are truly
eruptive; as a matter of fact, the present writer has never seen an
instance in which he was convinced that such was the case. Where the
pocks are very numerous, especially in subjects with an irritable
skin, much distress may be caused by the itching and by the
consequences of scratching, and marked febrile reaction may accompany
the process; so that, in view of the great similarity of the lesions
to those of the variolous eruption, much doubt is sometimes
entertained as to whether the disease is not really small-pox. This
question cannot always be definitely settled at first, but the failure
of the secondary fever of small-pox, together with the fact that the
disease does not spread by infection, will generally suffice to decide
it.
Concerning those cases of generalized vaccinia that are manifestly not
eruptive, it sometimes happens that the cutaneous receptivity is not
exhausted for several weeks, or even months. Such cases set Bryce's
test at defiance, in consequence, probably, of an idiosyncrasy. In
some of these instances the pocks appear in clusters of successive
formation, looking not unlike patches of zoster. Small supplementary
pocks in the immediate neighborhood of the original lesion are not at
all uncommon.
PATHOLOGICAL ANATOMY.--Avoiding the minute histological details for
which the prescribed length of this article gives no scope, but little
is to be added to what has already been said in the section on the
clinical features of the disease. The lesions of vaccinia are wholly
cutaneous. Confining ourselves to cases that follow a regular course,
there is, indeed, but one, the pock--a term that seems preferable to
vesicle and {463} pustule, since the latter apply only during certain
phases in the development of the lesion.
A pock may be regarded as essentially a lesion of the epidermis, for
it is in that structure that its most striking features are developed,
and in some cases, although doubtless the papillary layer of the derma
is congested, there is no permanent alteration of tissue below the
Malpighian layer of the epidermis. These are the catarrhal pocks of
Rindfleisch, and it is in such cases, if in any, that no scar (even of
temporary duration) results. The term catarrhal pock, however, is not
vitiated by an extension of the morbid process deep enough to produce
a permanent cicatrix, and it is probable that in most cases the
catarrhal type predominates. By the term diphtheritic pock the same
author refers to cases in which the congestion of the papillary layer
is so intense as to block the supply of blood to the apices of the
papillæ, as a result of which they become exsanguinated and necrosed,
forming a white pultaceous layer on the floor of the pock, which is
undoubtedly what Ceely referred to when he spoke of a false membrane.
In some cases even the subcutaneous tissue undergoes necrosis, a sort
of core being included in the substance of the crust that ultimately
forms.
Whichever of these forms of pock we take into consideration, always
excluding irregularities and complications, we find certain definite
changes in the epidermis. The dome of the pock is formed by the
unbroken transparent horny layer of the epidermis, unaffected by the
morbid process. The cavity of the pock is formed by the squamous cells
of the epidermis being forced out of their normal relations by an
exudation of lymph between them, some of them being tilted up edgewise
while still retaining their connection with the surrounding cells,
thus accounting for the multilocular structure of the pock; for it is
a fact that the circular bourrelet consists not of one ring-like
cavity, but of many separate chambers. The result of this structure
is, that the liquid contained within the pock--the lymph--escapes only
partly through a puncture made in the wall of the vesicle. In order to
evacuate the pock thoroughly it is necessary to make a great number of
punctures or a circular incision following the ring-like ridge of the
bourrelet.
The lymph contained within the cells of the pock is a liquid which in
its gross physical properties differs but little from the lymph which
exudes from any traumatic surface shortly after the injury has been
inflicted, as in the glazing process that takes place in wounds.
Examined microscopically, however, it is found to contain not only the
fibrin, the salts, the corpuscular elements, and the débris that
ordinary tissue-juice presents, but also certain minute spherical
bodies--termed microspheres, microzymes, vaccinads, etc.--that give it
its characteristic infective quality and justify the title of virus
commonly applied to it. That these minute bodies really constitute the
virulent element of the lymph, or at least that they are the vehicle
of the contagium, is not a mere matter of conjecture, but has been
demonstrated abundantly, notably by Chauveau and Sanderson's diffusion
experiments. Inoculation with the supernatant liquid, containing none
of these bodies, always fails to convey the disease, but it is not
absolutely essential that they should be present in large proportion
in the lymph to render the latter virulent, for Chauveau found that
lymph diluted with thirty times its bulk of water was not without
infective {464} power. It scarcely need be said, however, that the
greater the proportion in which they are present, the greater is the
probability that the lymph will prove infective on inoculation. These
bodies have been supposed to be of a vegetable nature, and Hallier,
Kohn, and others have bestowed no little study upon their botanical
characteristics. Under favorable circumstances they retain their
virulent properties for a long time, especially if kept perfectly dry
and not subjected to a high temperature. The present writer has met
with success in the use of vaccinal virus seven years old.
The lymph differs somewhat in its gross appearances according as it is
produced in man or in the bovine animal. In the former it is clear and
limpid, and exudes freely in great drops when the pock is punctured in
its peripheral portion; in the latter it is more straw-colored and
more viscid, exuding sluggishly, or even refusing to flow without the
aid of pressure. Moreover, the vaccinads seem endowed with different
properties in the two cases: in man they have a tendency to remain
equably diffused through the liquid, while in the cow they tend to
separate from it and to be deposited upon any solid surface at hand.
The phenomenon termed umbilication, common to the vaccinal pock and to
that of variola, has given rise to some differences of opinion as to
the mechanism of its production. The term implies a depression at the
centre of the pock. This appearance is not invariable, but it is
constant enough to have met with general acceptance as a
characteristic feature, notwithstanding the undoubted fact that it is
found in lesions that have nothing whatever to do with any of the
varioliform diseases. Not to waste space in discussing the various
theories that have found supporters, it may be said that they have all
been proved to be defective, save only the simple explanation that as
the process of evolution advances the centre of the pock undergoes
desiccation, whereby that portion of the tissue involved is so glued
and drawn together as to become incapable of the swelling that is
still going on in the growing peripheral portion of the lesion.
The crust into which the pock ultimately becomes converted is not, as
is commonly supposed, mere dried lymph and nothing else; it is dried
tissue enclosing concrete lymph. It generally includes also various
sorts of débris--broken-down epithelium, blood-corpuscles,
pus-corpuscles, and even, in rare cases, a core of sphacelated tissue
like that of a furuncle.
As has already been said, the cicatrix is to a certain extent peculiar
in that it is usually depressed and foveolated. Too much stress has
been laid upon these features, however, and the truth is that some
traumatic scars cannot be distinguished readily from that of vaccinia,
while, on the other hand, many a genuine pock leaves no permanent
trace behind it. Indeed, in the cow it is the exception for a
noteworthy scar to form.
SEQUELÆ AND COMPLICATIONS.--The most important sequela of vaccinia is
the fact that it protects the subject against small-pox, and on that
circumstance hinges the chief practical interest of the disease. This
leads us at once to the subject of vaccination, and therefore under
that head we shall pursue our consideration of this curious affection.
{465} Vaccination.
SYNONYMS.--"The new inoculation;" _Fr._ Vaccination; _Ger._
Kuhpockenimpfung, Schutzpockenimpfung; _It._ Vaccinazione; _Sp._
Vacunacion.
HISTORY.--Before giving the history of vaccination itself (meaning by
that term the intentional inoculation of vaccinia for the purpose of
protecting the subject against small-pox), it may be well to devote a
few words to a practice that preceded it--that of the intentional
inoculation of small-pox (or simply inoculation, latterly called
variolation). In very early times various Oriental peoples became
aware of the fact that small-pox might be very decidedly mitigated by
inoculation. This was practised in various ways, all of which may be
reduced to the process of inserting small-pox virus into a solution of
continuity. Lady Montagu, the wife of an English ambassador to Turkey,
brought the practice back to England with her, where it soon made its
way into popular favor, and whence it spread rapidly over Europe and
America. Thus contracted, small-pox was shorn of a great part of its
terrors; the eruption was usually trifling in amount, and in every way
the disease was mild as a rule. Still, the mortality was something
worth considering, and, worse than that, the inoculated disease was
communicable by effluvium, so that an inoculated person had to be
secluded carefully for fear of spreading the disease in the ordinary
way. In all cases, too, careful medical treatment was thought
necessary. On the whole, then, while inoculation was undoubtedly a
boon, it was fraught with many grave perils. So great, indeed, were
these perils, and so thoroughly were they appreciated, that the
practice was interdicted by law in most civilized countries so soon as
vaccination had become established in popular favor.