PETERS. — METABOLISM AND DIVISION IN PROTOZOA. 443 



It is almost entirely to this class of substances — and, it must be added, 

 to a particular phase only of this extensive subject — that my studies 

 have been directed. 



Much work has been done upon the relation of salts to animal cells, 

 the most of which bears orly an indirect relation to that which is here 

 attempted. In the experiments of mammalian physiology the principal 

 problem has been to find out the function of the salts in general meta- 

 bolism. The history of this subject is well given by Rywosh (:0O). In 

 another class of experiments the aim has been to determine what salts 

 are necessary for the development of the animal, or what is the influence 

 of salts upon that process. This is well illustrated by the extensive 

 work of Herbst ('93 to ? 99) upon marine Invertebrates. The Protozoa, 

 the group dealt with in the present paper, have been made the objects 

 of much chemical experimentation. But the relation between the p7-ocess 

 of division and salts physiologically present in organisms or their media 

 has received but little direct investigation. In Protozoa the division- 

 reaction, if so it may be named, has not been treated heretofore in a 

 numerical way as a criterion of the comparative effects of the physiologi- 

 cal salts, used either singly or in combination. Of interest in the present 

 work, so far as they bear on division, are the experiments upon artificial 

 fertilization with salts, as done by Loeb ('99), Morgan ('99), and Viguier 

 (:01). These questions suggest themselves: In what relation do the 

 salts normally stand to the process of division, and is their action osmotic, 

 or chemical, or both? The analogy between the egg-cell and the pro- 

 tozoan has been frequently stated. The present work was suggested by 

 one feature of the mode of differentiation in the embryo. Unequal rate 

 of division is seen to be an important factor in determining the relative 

 positions of parts in the embryo. Our ignorance of the special factors 

 involved here is well expressed by Minot (:03, pp. 38-39). " The reason 

 for the unequal growth is unknown. "We have not even an hypothesis to 

 oiler as to why one group of cells multiplies or expands faster than 

 another group of apparently similar cells close by in the same germ layer. 

 It is no real explanation to say that it is the result of heredity, for that 

 leaves us as completely in the dark as ever as to the physiological factors 

 at work in the developing individual." This question naturally arises : 

 To what extent, if any, is the rapidity of division influenced by normal 

 chemical factors, especially the ever present physiological salts? A 

 protozoan was selected as the object because it seemed to present fewer 

 complications with other possible factors than exist in the case of an 

 association of cells. 



