498 STUDIES IN GENERAL PHYSIOLOGY 
and pathology demand that the systematic development of 
comparative physiology be one of the physiological problems 
of today. 
I may be pardoned for calling attention to one special field 
of comparative physiology which I believe to be especially 
fertile. I refer to the field of physiological morphology. 
I applied this name to the investigation of the connection 
between the chemical changes and the process of organiza- 
tion in living matter. Two series of facts allow us to connect 
these two groups of phenomena: (1) the fact that phenomena 
of fermentation lead to an increase in the number of mole- 
cules, and thus bring about an increase of osmotic pressure in 
the cells, this increase of osmotic pressure being the source 
of energy for the work of growth; (2) the facts of hetero- 
morphosis, 7. e., the possibility of transforming in certain 
animals one organ into another or substituting one organ for 
another through external influences, such as gravitation, con- 
tact, light, etc. 
The exact and definite determination of life-phenomena 
which are common to plants and animals is only one side of 
the physiological problem of today. The other side is the 
construction of a mental picture of the constitution of living 
matter from these general qualities. In this portion of our 
work we need the aid of physical chemistry and especially of 
three of its theories: stereochemistry, Van ’t Hoff’s theory 
of osmotic pressure, and the theory of the dissociation of 
electrolytes. We know that the peculiar phenomena of oxi- 
dation in living matter are determined by fermentative pro- 
cesses, and we venture to say that fermentations form the 
basis of all life-phenomena. It has been demonstrated that 
fermentability is a function of the geometrical configuration 
of the molecule. Saccharomyces cerevisic is a ferment for 
such sugars only as have three or a multiple of three atoms 
of carbon in the molecule. Among the hexaldoses only 
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