METABOLISM 223 



The reciprocal relation between dissociation, osmotic pressure, and 

 the freezing-point of a solution presents a ready way of finding the 

 osmotic pressure of any solution without testing it directly, and to deter- 

 mine its freezing-point is much simpler. The greater the dissociation, 

 and so the more molecules a solution contains, the greater is its pressure 

 and the lower its freezing-point. A gram-molecular solution is one con- 

 taining as many grams dissolved as there are units in its molecular weight. 

 Such a solution wherein no dissociation occurs has been found to 

 lower the freezing-point 1.86 C. If, then, we find by means of an 

 apparatus for the purpose how much lower than that of pure water is 

 the freezing-point of the solution whose osmotic pressure is desired, 

 we need only to divide the fraction of a degree of the lowering (expressed 

 A) by the constant 1.86 to have the desired percentage of the lowering 

 of the osmotic pressure. A gram-molecular solution of a non-electrolyte 

 (no dissociation) exerts a pressure of 22+ atmospheres, and the per- 

 centage of lowering of the pressure found multiplied by this number gives 

 the osmotic pressure desired in atmospheres. The pressure is propor- 

 tionate to the concentration, a 2 per cent, solution of an electrolyte 

 pressing twice as much as a 1 per cent, solution of the same substance. 



By the freezing-point method we may, then, determine not only the 

 osmotic pressure of any solution, whether an electrolyte or not, but also 

 the degree of its electrolytic dissociation in case the solution be an electro- 

 lyte. This latter datum seems often to be of essential importance as 

 regards the effects of saline electrolytes on protoplasm. 



One of the most surprising things to the student of these matters at 

 first is the great pressures exerted by solutions of this sort. Osmosis is 

 clearly one of the great forces of organic nature, and it acts everywhere 

 in plants and animals, and yet so quietly as to remain unsuspected save 

 in its effects until the refinements of modern physical chemistry made it 

 manifest. 



"VITALISM." This term is sometimes useful in biological discussions, 

 but its meaning nowadays is much less significant than it was fifty years 

 ago when the principles of physics and of chemistry had not as yet been 

 applied to living processes. Indeed, the term vitalism then implied 

 distinctly that organic reactions (absorption, secretion, etc.) were char- 

 acteristic and unique, and essentially different in kind from those outside 

 of living protoplasm. Today we know or at least think we know in 

 what ways the vital processes are characteristic arid different namely, 

 in their subtlety, complexity, and intricacy of interaction, and so far as 

 we know only in these ways. Vitalism, then, today means only the sum 

 total of the chemiphysical reactions of vital matter. Whether these will 

 be known in detail sometime cannot be foretold. The important thing 

 is that their nature is such that they might be known in detail were our 

 methods refined enough, when without a doubt they would be found to be 

 in kind like the rest of Nature. 



THE PHENOMENA OP SECRETION are the secretory events so far as 

 study of secreting and absorbing epithelia reveals them to us through 



