148 Tue Microscope. 
does exist in greatest abundance, maturity and virulence in the 
saliva and salivary glands of rabid animals, and that these are 
the proper or more promising subjects for investigations by 
inoculation, cultivation and microscopy. 
Much has been said and written for and against Koch’s 
comma bacillus as the cause of cholera. All bacilli are vege- 
table in nature. They are flowerless plants, but devoid of 
chlorophyl; they do not subsist as most other plants do, by the 
decomposition of carbonic acid gas, but take oxygen direct 
from the atmosphere and the pabulum in which they live. 
Some of them are endowed with power of passive motion, but 
to none of them so far as I know, nor to their spores, have 
been attributed self-propelling powers for aerial navigation. 
Their transportation is accomplished by accident and by atmos- 
pherical currents. I submit the question as to whether the 
history of cholera invasion and spread accords with such 
agencies. 
With a sort of home upon the Ganges, in the form of an 
almost perpetual endemic, it occasionally becomes in some 
sense migratory and epidemic in nearly all parts of the world. 
The lines of its ravages do not correspond to the varying cur- 
rents of the atmosphere, nor to accidental forces. The history 
of these epidemics shows a movement from place to place 
with some regard to regular succession as to time, and to 
constancy as to direction, and with but secondary regard to 
prevailing winds or to geographical obstacles. Dr. Snow 
detailed the movements of one epidemic of this disease with 
perhaps as much faithfulness as any that has been published. 
Breaking out at Jessore, it proceeded to Calcutta, from where 
it radiated simultaneously in three distinct lines, one south- 
west to Madras, another south-east along the opposite coast of 
the Bay of Bengal, and a third north-west along the valley of 
the Ganges. These streams of pestilence, in their several 
directions, pursued the even tenor of their way, halting and 
again breaking out at irregular intervals at nearly every step, 
until they well-nigh enveloped the earth. 
The same general facts will appear in tracing the course of 
some other epidemics of this disease, which any one can do at 
leisure. 
