50 
appear to follow heavy rains, and it has been suggested that 
the pathogenic microbia may be present in overflows of 
stagnant water, or may be washed into pools of water tem- 
porarily formed ; so, that, when these dry np, the germs are 
blown with the sediment into the atmosphere and inhaled, 
or deposited in milk or other beverages. As such conditions 
imply, however, not only the presence of abundance of fresh 
air, but also sunlight (to the hygienic action of which latter I 
am about to refer), the supposition is rather against the re- 
sults of the experiments under consideration. If, however, we 
assume the presence of pathogenic germs in the foul atmos- 
phere of ill-ventilated sewers, then heavy rains, or any other 
condition which diminishes the air space in the sewers, will 
force out more or less dense volumes, or gusts, of sewer gas, 
and the germs be conveyed directly to their new medium of 
culture, whether in the bodies of men or animals breathing 
such gases, or in the beverage which they infect ; and they 
will be protected during their passage from the attenuating 
influence of fresh air by the appropriate environment which 
transports them. 
We come now to the influence of light and darkness on 
micro-organisms, concerning which the results of some very 
interesting experiments, carried on independently by M. 
Duclaux and M. Arloing, have lately been made known. I 
proceed to consider these with the more pleasure, as they 
afford me an opportunity of again referring to one of those 
suggestive and thoughtful utterances which abound in the 
writings of our late revered member. Dr. Angus Smith. 
Deferring to the fact that fevers have not been traced to 
open rivers, or to putrefaction in the open air, though they 
have been traced to decomposition taking plane under cover, 
as in sewers. Dr, Smith observes in a paper published in 
1880 : “The question arises. Is this owing to the concentra- 
tion ; or to the difference of decomposition in darkness ; or 
to the better supply of oxygen ? The effect of sunlight in 
