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the intestinal canal. Hydrophobia may be taken as an example 
of what I wish to express, although, of course, a perfectly distinct 
disease. A person bitten by a dog suffering from hydrophobia is 
innoculated with the poison by its being directly conveyed to the 
circulation by the bite, and the result would be, in all probability, 
fatal; but if the same virus had even been swallowed, it would 
have had no effect. And what do we find? When a person is 
bitten in this way, instinct tells him to suck the wound, and it is 
unquestionable that if this could be done immediately, it would 
be a successful antidote, inasmuch as it would remove the poison 
from the circulation, while it would have no effect even if swal- 
lowed. 
You will observe, therefore, why it is concluded that certain 
zymotic diseases are chiefly spread by air, while others are spread 
by water, because the germs of the one—the former—act when 
they enter the blood direct, while those of the other act after 
passing through the stomach. 
The question of the production of cholera, from its evident 
connection with impure water, has lately engaged the attention of 
chemists and microscopists very much. I shall endeavour to state 
briefly the conclusions which have been arrived at. The most 
serious outbreaks occurred in the years 1832, 1849, 1854, and 
1866, and London in each case suffered; so that the fact may be 
stated by the way, that rivers and wells were the sources of the 
water-supply, and that both were of an inferior character, The 
conclusions arrived at on the first occasion may be passed over, 
but on the second—in the year 1849—we find that Dr. Snow — 
made an important observation. He found that the water derived 
from a certain well had in many instances been the immediate 
channel through which the contagion had been conveyed. This 
was no doubt one of the first matters which brought the relation 
of water to disease prominently forward, and suggested the 
importance of water-analysis ; though the latter cannot be said to 
have been much attended to till later years. More recently Mr. 
Simon, the Medical Officer of the Privy Council, remarking on 
this subject, says, “It is, I believe, a matter of absolute demon- 
