j^SSTisef ] Great Pathological Processes. 19 
is positive contains the entire truth, until we see that there are 
other facts to be included. You see that in following the migration 
of the cholera poison, I am contemplating events which admit of 
chemical consideration. I shall afterwards show you that cholera 
evacuation or rice-water is a particular fluid which has no equal in 
any other fluid as regards the kind and rapidity of its decomposition ; 
that during decomposition it undergoes changes which are also of a 
specific kind ; and that this fluid so changed reproduces the entire 
process. In addition to the direct poison, there must be certain 
favouring circumstances before cholera can be developed. Among 
these is impure drinking-water. We have the epidemics of the 
year 1848-9 here in London; 1854-5 also in London ; and again 
the epidemic of 1866 in Whitechapel. In all these it has been 
clearly proved that a population which drinks impure water, or 
water containing a very large amount of putrescible or putrescent 
organic matter, is twice or three times as liable to be infected with 
cholera as a population drinking pure water ; and not only that, but 
if a population is thus affected with cholera and drinks impure 
water, its mortality is twice or three times as great as the mortality 
in any other choleraic epidemic which occurs in a place in which 
the people drink pure water. You can take these facts as axioms ; 
but do not therefore venture upon the conclusion that in every 
case of cholera it has been the drinking-water which has caused the 
predisposition. There may be others of which we are not yet 
aware, and which we have to study ; but where we find those facts 
so well proved as they have been here in London, we have a certain 
right to assume that this was the main predisposing cause. 
We find impure air to be a means of the distribution of cholera, 
and an element of predisposition. What is there easier than that 
in the house of a poor person a quantity of vomit from a cholera 
patient should go behind the bed, along the wall, and make a little 
pool in a crevice of the floor where it is not wiped up ? It is not 
disinfected ; it stands there and putrefies, the more easily as these 
alkaline matters have a peculiar hygroscopic power, which enables 
them to attract water in sufiicient quantity to resume their decom- 
position even after they have been apparently quite dried. The 
bed is afterwards moved by other people ; a dust is raised, and with 
that dust a small particle of the dried substance is carried up, and 
the consequence is that a person who before was not affected, now 
breathes that dust and gets it into the mouth, swallows it, and 
becomes aflected by cholera. Thus, the impure air and the dust of 
the house become carrying and predisposing agents for the propa- 
gation of cholera. 
The consideration of impure food will lead you to the same 
result. If persons eat with dirty hands, and are in the neigh- 
bourhood of cholera patients, or of impurities such as I have now 
c 2 
