CONTAGION AND INFECTION. 
645 
contaminates or pollutes, the word contagium might be Angli- 
cised as effluvium has been. The contaminating agents of 
disease would be spoken of in the following manner, — as 
contagium variolae, contagium scarlatinae, contagium rubeolae, 
&c., and where required plurally, contagia as effluvia. 
Wherever the agents of communicable diseases have been 
demonstrated, they have uniformly been shown to depend 
upon some form of cell-life. Diseases are communicable in 
three modes : — First, by inoculation ; secondly, by deposit 
on the integumentary or mucous surface ; and, thirdly, by 
ingestion either to the stomach or lungs. The analogous 
modes of vegetable propagation are grafting or budding, 
sowing the seed, and accidental diffusion. For the manifes- 
ation of a wide-spread epidemic three things are necessary: — 
First, the presence of a special poison ; second, an adaptation 
of the community for the reception and specific action of the 
poison ; and, third, favouring atmospheric and telluric con- 
ditions. He referred to the fact, that all pestilential diseases 
were communicable, and objected to the prevalence of 
qualifying expressions, such as “ contingently contagious,” 
&c . If a disease ever merits the term contagious or in- 
fectious, the property of the disease under all circumstances 
remains the same; the contingencies have regard to the 
manifestation of the properties of infectious agents, but not 
to the diseases engendered by those agents. Smallpox is 
still a contagious disease, though it does not now appear 
among us as an epidemic of fatal virulence, and very 
commonly dies out in places where it occurs without 
spreading among the population. The disease is the same, 
but the conditions which favoured the development of the 
poison have been changed. He condemned also the too free 
use of the terms epidemic foci, influence, and force, as cal- 
culated to divert the mind from the all-important inquiry — the 
nature and properties of the morbid poisons ; for all the 
advantages which had accrued to mankind from the study of 
infectious diseases were traceable to the knowledge acquired 
of the agents of disease in their operation on the body. 
Allusion was made to the uncertainty which surrounded the 
subject of the diffusion of disease, and instances given to show 
that contagion and infection were not uniform actions. 
Ambiguous cases, which seemed to indicate a generation 
de novo of the specific poison, are explicable on other and 
more rational principles. He suggested that a wider view 
should be taken of contagion and infection, and quoted from 
the Reports of the Board of Health, from which it appeared 
that limited notions on this subject led necessarily to the 
