PETERS. — METABOLISM AND DIVISION IN PROTOZOA. 487 



both of which are exerted by the same substance at a given concen- 

 tration. Because the latter factor depends upon the nature of the sub- 

 stance whose native properties come to act physiologically when that 

 substance forms an essential, that ?'s, a constitutive "proportion of the living 

 organism, and because I shall need a well-defined term to express this 

 relation, I shall denominate it the factor of constitutive proportion or, 

 here, simply the constitutive factor. The idea of proportion will have 

 importance in the next section. 



Substances which act by virtue of being in the organism form a 

 general series of some range with respect to the constitutive and osmotic 

 factors. If the substance is actively toxic the osmotic factor becomes 

 practically nil, the constitutive factor accounting for nearly the whole 

 result. A modification of the permeability of membranes through altera- 

 tion of constitution, which may possibly be important in toxic action, I 

 reckon of course with the constitutive factor. At the opposite end of 

 the general series there is a class of substances, here called the physio- 

 logical salts, which were once considered to be practically inert (ash) 

 constituents of the organism. But investigations beginning with Liebig 

 have shown the necessity of a different interpretation. Their importance 

 as osmotically active substances is now demonstrated. But their consti- 

 tutive, metabolic activity, although evidently present, is practically un- 

 known, so far as regards its mode of action. To the question, what is 

 the chemical activity in the case of each salt, physiology is at present 

 able to give but very uncertain answer. Suggestions as to what these 

 activities may consist in are to be found in Rywosh (: 00). 



We are now prepared to consider some peculiar conditions in our 

 experiments, made evident by analysis. When the animals were con- 

 tained in a medium of distilled water, there existed within each the 

 several partial pressures of their physiological salts. On the outside of 

 the organism respective partial pressures to balance the former were 

 absent. Salts were withdrawn and the animals died in consequence. 

 Upon the other hand, when Stentors were placed in a hyperisotonic 

 medium of pure milk sugar exactly the same unbalanced partial pressures 

 existed within the cell, yet they did not die for the want of salts. In 

 fact the animals suffered no appreciable harm from the milk sugar me- 

 dium. The same unbalanced partial pressures existed when a single 

 hyperisotonic salt was applied, excepting for the single salt in question. 

 Death resulted mainly from a penetrating excess of the salt applied. 

 First, how shall we explain the contrasting effects above referred to 

 between milk sugar and distilled water ? Evidently some other condi 



