262 NATURE AND LIFE. 
own structure, its specific energy, its mode of nutrition, its 
fixed secretions—characteristics, moreover, which vary with 
circumstances and media. . Yet we can point out more than 
one interesting similarity between certain ones of these 
species, which seem to discharge quite distinct functions, 
and hold very unlike stations, in the vast harmony of vital 
monads. The cells of fruits, when placed in certain condi- 
tions, behave, as has been seen, like the cells of brewer’s 
yeast; they both decompose sugar and yield alcohol. We 
may trace resemblances not less close, as Blondeau and 
Pasteur have done, between acetic mycoderms and blood- 
globules. Both alike serve as carriers of oxygen—the first 
for the slow combustion of alcohol; the last, for the slow 
combustion of the albuminoid matters in animal tissues. 
It is even likely that there is a principle in mycoderms 
similar to hemoglobine in the blood-globule, and provided 
with a special affinity for oxygen. However this may be, 
comparisons of this kind open a new path for physiology. 
As that science is definitely summed up in the explanation 
of existences and processes in the microscopic elements of 
organs, it is plain that nothing can be more useful to it 
than the study of these one-celled organisms in which the 
phenomena are extremely simple, and life is reduced, in a 
manner, to its primitive factors. It becomes more and 
more evident that progress in the comprehension of the 
superior animals is bound, with the very closest ties, to ad- 
vance in the comprehension of the mechanism of nutrition 
in the rudimentary units of life, in the smallest beings that 
it is given us to study. 
IT. 
Now, whence come those organized microscopic corpus- 
cles to which, as we have seen, very many of the alterations 
of organic matter must be attributed? Upon this great 
problem, opinions at this day are still very contradictory. 
