470 VESICULAR DISEASE CONTRACTED FROM SHEEP. 
and introduced either into the blood-vessels or into the tissue 
of another animal, by a process which we call inoculation ; and 
at other times it would seem that the poison is merely con- 
veyed from the surface of the diseased animal to that of the 
healthy person by contact — what we commonly call con- 
tagion . Or this animal poison may be of a volatile nature ; 
it may be susceptible of solution or suspension in the atmo- 
spere, and may emanate from the sick either by the breath, 
or by cutaneous exhalation ; or by effluvia from alvine and 
other secretions : and thus it may effect those who come 
within certain range either of the sick man or diseased animal. 
All these diseases arising from animal poisons, and propa- 
gated either through inoculation, or contagion, or infection, 
appear to be subject to certain general laws ; and to these, 
perhaps, I may as well advert before I bring under your no- 
tice a very remarkable case of disease resulting from the in- 
troduction of an animal poison by means of inoculation. The 
poison in the case to which I allude was derived from the skin 
or from the other parts of the sheep’s head, and introduced into 
the system by means of a butcher’s knife. The general laws 
to which I have just alluded as governing those diseases de- 
pendent upon animal poisons, are more especially applicable, 
of course, to those poisons which are generated within the 
human body; although if we had greater knowledge of the 
diseases which result from poisons generated within the 
bodies of brutes, the same or analogous laws would probably 
be found to hold good also in them. 
First, then, with respect to these laws relating to animal 
poisons, we observe that each peculiar poison has the power 
of exciting certain definite and specific actions when intro- 
duced into a healthy organization. And secondly, there 
appears to be a period of latency, a period of incubation in 
the system (varying in different poisons,) before the specific 
morbid actions are set up in the healthy system into which 
the poison has been introduced. And, thirdly, we observe 
that the specific morbid effects resulting from the introduction 
of the animal poison vary somewhat in different individuals, 
apparently varying according to the intensity of the poison — 
the dose of the poison, I may term it, imbibed, and the pre- 
disposition of the individual infected. Now, these laws to 
which l have thus adverted are particularly exemplified in 
cases of variola and rubeola, scarlatina, and typhus, accord- 
ing as these diseases occur sporadically or in the course of 
epidemics. Each of these animal poisons is productive of 
certain definite local morbid actions, which are not accidental 
but governed by certain laws. Some of these poisons, we 
