WATER DEFICIT AND THE ACTION OF VITAMINES, AMINO- 
COMPOUNDS, AND SALTS ON HYDRATION^ 
D. T. MacDougal 
(Received for publication January 17, 1921) 
It is well known to any one who has seriously examined cells in a living 
condition that protoplasm is a viscous substance which at different times 
or in different parts of the same protoplast may vary in consistency from a 
liquid to that of a firm jelly, a behavior characteristic of an emulsoid colloid. 
This term in the present instance is applied to substances which in a con- 
dition of hydration exist in two distinct phases in the mass; in one, a few 
or many molecules of the solid substance are combined or held together by 
adsorption with a relatively small number of water molecules to form a 
denser phase, which in the more liquid condition of the mass floats in or is 
surrounded by a more fluid phase in which the solid particles sustain a 
much smaller proportion to the water. 
If we begin to form our picture of the colloid in this condition, which 
would be that of melted agar or gelatine, we shall be ready to follow its 
transformation to that of a jelly by visualizing an action by which the 
surface tension of the aggregates of molecules is increased by lowered 
temperatures or other causes, the aggregates coming together to form mesh- 
works or honeycombs, running through or partially enclosing the material 
of the more liquid phase. The possibilities implied in the reversal of these 
phases, important as they may be, may be disregarded during the present 
discussion. 
Living matter is anything but such a simple substance. The results of 
all of our examinations by physical and chemical methods are to the effect 
that the living matter of plants includes the following groups of substances 
which may assume the colloidal conditions described above: First, the 
nitrogenous substances, which include not only albumin and all its deriva- 
tives, but also synthetic compounds. Next in importance, and constituting 
perhaps the greater part of the mass, are the pentosans or mucilaginous 
sugars which may be formed in carbohydrate metabolism in any part of 
the mass when hexoses are converted into pentoses and these are condensed 
into the pentosans by dehydration. The presence of sucli fatty acids as 
stearic, palmitic, and oleic, and the readiness with which they form soaps 
by combination with potassium, sodium, and magnesium, make it also 
certain that such substances are an invariable component of the biocolloids. 
^ Invitation paper read before the Physiological Section of the Botanical Society of 
America, in the symposium on biophysics, at Chicago, December 28, 1920. 
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