536 TRANSACTIONS OF THE CANADIAN INSTITUTE. [Vov. VIII. 
progressed at all. Comparative Pathology has been the path which has 
led to the most fruitful acquisition of new and useful knowledge. Disease ~ 
phenomena, broadly, are the same throughout the whole animal kingdom 
and, even in their finer details, they are the same among the higher animals. 
But, while this is true, there are differences which exist between one group 
and another, and, in regard to individual diseases, we find the most sur- 
prising limitations in their distribution. This is true of all disease, but 
it is especially true of infectious and parasitic diseases and although we 
find similar organisms producing similar disease in related groups of 
animals, yet, for many infections and parasites the boundary of the 
genus or even of the species is often an insurmountable one and we realize, 
that, with the evolution of a species, there has gone hand in hand with 
it, the evolution of its diseases. It must not be imagined, of course, 
that this is a universal law. Many animal diseases may be transmitted 
to man. Rabies, for instance, infects the human as well as the canine 
species. ‘The whole mammalian group may be infected by this organism, 
yet Pasteur showed, in his early work upon Rabies, that the disease 
picture assumes different forms in different animal groups and especially 
shows marked variations in its incubation period, as it is passed from 
one group to another. On the other hand, there are many diseases, 
of which Leprosy is a good example, which, as far as we know 
at present, are entirely confined to the human race. In others, as for 
example, the Trypanosome infections different species infect man from 
those which infect other animals, in man producing the disease called 
Sleeping Sickness, in horses and other hoofed animals the various forms 
of Tsetse Fly Disease, yet the organisms are closely related and the same 
underlying phenomenon of transmission is present, that is by an inter- 
mediate insect host. 
These facts present interesting problems in evolution and we cannot 
examine them without the question pressing upon us: what has been the 
influence of these diseases upon animal evolution, and how has animal 
evolution influenced the disease? 
The subject which I wish to discuss this evening, is that of the evolu- 
tion of human disease and its connection with the evolution of the race. 
In discussing this subject, there are two distinct sides to be considered: 
first, the evolution of human disease, i.e., the influence upon the cause 
of disease in man, of the change in the structure and environment of the 
human race in its evolution from the anthropoid to man, and second, 
the influence of human disease upon race evolution. The first must of 
necessity be as yet much a matter of theory, because, in the first place, 
we can say practically nothing of the diseases of our earliest human an- 
