146 Tue Microscope. 
peutics, as well as hygiene. Our text-books are our witnesses. 
But accepting the germ theory of disease as the true one, we 
have presented a subject for microscopy far beyond the sub- 
jects of tissue structure and tissue change in point of abstruce- 
ness and value as well, which has been but little more than 
fairly entered. There is here among the subtle agents of con- 
tagion and infection an unlimited domain where the microscope 
must be the chief or only guide. While much of great value 
has already been brought to the surface, it is impossible to pre- 
dict the future importance of medical microscopy with object- 
ives of the more refractive glass recently brought out, and the 
improved methods of culture, isolation and inoculation. It 
may be profitable therefore on such an occasion as this to open 
for discussion some questions pertaining to manner of inquiry 
for facts which appear to lie beyond the boundaries of our 
present knowledge; for well considered and systematized pre- 
liminaries are even more essential in these undertakings than 
in any others. The biological nature, habitat and habits of any 
given poison should be studied as far as possible from a recog- 
nition of all the general conditions or circumstances or phe- 
nomena, attending its manifestations, and these formulated to 
be used as guides in further studies. As bearing upon the sub- 
ject, I venture to offer two propositions: 
First—That a disease poison, if originating or propagating 
within the body, is most abundant, mature and virulent, in- 
connection with the tissues, secretions, solids or fluids, which 
furnish a natural pabulum, and hence in this connection it will 
be most susceptable of discovery. 
Second—That the study of any given disease poison as far 
as possible from the general conditions or circumstances at- 
tending its action, furnishes valuable suggestions for pro- 
_ceedures, and in some measure points to the biological nature, 
habitat, habits and physical attributes of such poison. 
If these propositions have been well considered, it would 
appear to be pertinent to inquire whether the recent studies 
relating to the infections of rabies and of cholera have been 
wisely directed by what has been regarded as settled facts de- 
duced from general observations. 
In the veterinary school of Berlin more than fifty years 
