INFECTIVE AND CONTAGIOUS DISEASES. 19 
M.B.C.V.S., Veterinary Officer to the Institution, and to Dr. 
Sanderson, while Mr. George Fleming has kindly supplied him 
with material from abroad. Having served on the recent com¬ 
mittee on septicaemia and pyaemia, he had examined these 
diseases very closely, and since they, though rare, are not un¬ 
known in the higher classes of lower animals, he appreciated the 
value of investigations of them in these animals, where certain 
complicating elements of this study in man are absent. He pro- 
posed, in the first place, to examine the relations of Bacteria to 
disease, and thought that at present there is much confusion in the 
views with regard to the relations of these organisms to contagion. 
In studying the general pathology of contagion we have to do 
with its nature, mode of action, and methods of reproduction and 
communication, as leading to general laws. But in examining 
the intimate pathology of contagion , each disease and each con- 
tagium must be investigated on its own merits, the causes of 
latency and of incubation and the means of preservation of the 
poison outside the body being especially important. The diseases 
to be treated of may be divided into—(I) specific contagious fevers 
which are not known to arise de novo , but always are communi¬ 
cated from one animal to another. Of these the virus is usually 
most intense in some special fluid or tissue, and it is destroyed 
by putrefactive processes. Its effects once manifested in the 
system successfully resisted, future immunity, temporary or 
permanent, results. There is no absolute line of demarcation 
between these and the (II) so-called infective diseases, such as 
pyaemia, septicaemia, and traumatic erysipelas. In them there 
is no true period of latency nor specific lesion, and they tend to 
produce changes of the tissues allied to putrefaction. They 
generally arise de novo, and spread by infective processes from the 
seat of inoculation. They can be transmitted to all species of 
animals, whereas those of the first class affect special animal forms. 
The view of the particular nature of contagium is now 
generally allowed, but there are many hypotheses as to its true 
nature. Putrescence is looked upon as one of its sources, and 
there is now a generally current belief that contagion depends 
in some way on Bacteria both in acute specific diseases and 
infective disorders. We may pursue this supposition still 
farther and say that if Bacteria have anything to do with disease 
probably each disease has a special organism, each of these 
specific forms belonging to a distinct species and having its 
own morphological characters, that we may possibly be able 
to isolate and cultivate these distinct forms, and by ascertain¬ 
ing what conditions are prejudicial to them, lay the foundations of 
a true system of preventive medicine. They may be studied in 
blood or lymph, by reproducing them in the animal system, or in 
