47 
structure, or of weak breathing habit, or of persons spending 
much time in a vitiated atmosphere, engaged in dusty 
occupations, or suffering from bronchial catarrh, presented 
the requisite conditions of culture, assuming the presence of 
the germs of organisms which might otherwise discharge a 
useful function in the chemistry of life, possibly even in the 
chemical function of the lungs themselves. Dr. Angus Smith 
had also pointed out {Rivers Pollution Report, 1882,) that 
the putrefying process, when carried on in open rivers, such 
as the Clyde, does not seem to produce any marked form of 
disease ; whereas the gases escaping from covered sewers are 
apparently associated with specific zymotic maladies ; and 
he had suggested that “ we require to learn whether any 
of the germs of disease, or which germs, will live in 
an abundance of good air.” Dr. Smith had hinted that 
possibly the relative harmlessness of putrefaction in open 
rivers was a consequence of the less concentration of the 
resultant gases, or the more thorough putrefaction, oxida- 
tion, and destruction of the organic substances. Looking 
at the question from the biological, rather than from the 
chemical standpoint, it seemed to me that with all these 
ideas fioating about, and especially after the discovery of 
Koch’s tubercle bacillus, there was considerable foundation 
for the suggestion that possibly certain gases might have an 
influence in converting micro-saprophytes into micro-para- 
sites, and it did not seem a long step from this primary 
thought to the idea that carbonic acid might be such a gas. 
As the carbonic acid idea was, therefore, in the words of 
Touchstone, “ all ill-favoured thing, but mine own,” I may 
be permitted now to direct attention to a foot-note appended 
to M. Pasteur’s paper on a method of preventing hydro- 
phobia after infection, read before the Paris Acad^mie des 
Sciences on the 2Gth ult. M. Pasteur describes his method 
of attenuating the virus present in the marrow of rabbits 
which have died of rabies, by suspending portions of the 
