113 
Dr. Leone experimented also with water saturated with 
carbonic acid under pressure, and records the result as 
follows: “In these researches it was found that whilst in 
the non-carbonic water the number of microbia rose in five, 
ten, and fifteen days from hundreds to thousands per c.c., in 
the carbonic water the number of microbia not only did not 
increase but it 'diminished. In five days the number of 
organisms had fallen from 186 per c.c. to 87 ; in ten days to 
30 ; and in fifteen days to 20.” 
Dr. Leone applied other tests and came to the conclusion 
that the carbonic acid is the sole agent which interferes with 
the life of organisms in carbonic waters. 
One or two inquiries suggest themselves to me in con- 
nection with these very interesting observations. In the 
first place can we safely accept the mere numbers of the 
microbia as an expression of their chemical activity ? Thus, 
taking Dr. Smith’s hydrogen test, the quantity of hydrogen 
given off is regarded as an indication of the relative impurity 
of the water. But would a greater evolution of hydrogen 
be necessarily associated with a greater number of microbia ? 
Pasteur has called attention to a remarkable peculiarity in 
the life-history of microbia, observed during his ex|)eriments 
with the beer ferment. In the case of all other living 
creatures the weight of nutritive matter assimilated is pro- 
portionate to the weight of food consumed. In the case of 
alcoholic fermentations, however, the quantity of yeast 
formed is not proportionate to the quantity of sugar decom- 
posed, but varies according to other conditions, noticeably 
the abundance of free oxygen. Thus for a of yeast formed 
the weight of sugar decomposed in the process may be. 10(X, 
20(X, lOOa, or even more. Much depends in this respect. 
M. Pasteur argues, upon whether the yeast— or the microbe 
—has the vigour of youth or the decrepitude of senility. 
The cells of yeast, he tells us, in order to multiply in a 
fermentable medium in the absence of free oxygen, must be 
