114 
young and full of life and health ; if older, they have much 
difficulty in reproducing themselves in a milieu deprived of 
free oxygen. For the reasons already given, therefore, it 
would appear that the mere quantity of microhia reproduced 
in a given time may not be a test of the relatively innocuous 
character of the water or of the chemical activity of the 
organisms present. The quantity of hydrogen given off 
would apparently be a test of the latter, and it seems not 
improbable that, at least in some cases, the pathogenic 
virulence of microhia may be proportionate to the chemical 
activity set up rather than to the reproductive activity. 
The inquiry suggests what is, to me, a rather startling 
thought, and that is whether we may not arrive at a method 
of treating zymotic diseases by actually feeding the specific 
microhia, or, in other words, supplying them with appropriate 
means of existence, and thus diminishing their pathologically 
destructive action. If we follow out this line of reasoning 
it does not appear to follow necessarily that because, 
according to Dr. Leone, carbonic acid interferes with the life 
of organisms in water, or, in other words, arrests their muh 
tiplication, therefore it is a hygienic agent. Much must 
depend on the character of the organisms. Such a condition 
may simply eliminate the weaker or older organisms, and 
even accumulate their vital energy in those which remain. 
In dealing with this mysterious field of research, where 
there is still so much to tempt the investigator, I may, I 
hope, be pardoned for asking whether under certain circum^ 
stances a quantitative diminution of the microhia may not 
be consistent with a qualitative increase in regard to the 
capacity of the remainder for work ? 
