22 A. W. GREELEY. 



the colloidal particles, they always move toward the point at 

 which coagulation occurs. 



All these experiments seem to show that the structural changes 

 produced in protoplasm by thermal, osmotic, chemical or electri- 

 cal changes are the same, because all of these variations in the 

 external conditions act upon protoplasm only by altering the 

 physical state of its solid elements. Thus in the case of Para- 

 mcecium, at least, the structure of the protoplasm is seen to be 

 not fixed and uniform, but to depend directly on certain external 

 conditions and to vary with their variations. The best expression 

 of this behavior of protoplasm is found in the laws of the reaction 

 of colloidal solutions to external conditions. 



EFFECT OF THESE STRUCTURAL MODIFICATIONS ON THE VITAL 

 PROPERTIES OF THE PROTOPLASM. 



Having determined the changes produced in the structure of 

 the protoplasm by various chemical agencies, it remained to ascer- 

 tain how these structural changes modify the vital properties of 

 protoplasm. How far may a particular state of protoplasmic ac- 

 tivity be correlated with a given physical condition of protoplasmic 

 structure ? Or does the reaction of an organism as a whole to 

 an external stimulus depend in any measure upon the effect that 

 stimulus may have on the structure of the protoplasm ? 



/. Groivth and Cell Division. 



The rate of cell division may be taken as the best indication of 

 the general protoplasmic activity among the Protozoa, after the 

 method adopted by Calkins 1 in his work on the " Life Cycle of 

 Paramoecium." A quickened rate of cell division means an increase 

 in the metabolic activities of the cell. A condition of slow meta- 

 bolism is indicated by the cessation of cell division and the trans- 

 formation of the motile cell into a spore or cyst or other resting 

 stage. It has been already shown, in a paper - on the reactions 

 of various protozoa to variations in the temperature, that pre- 

 cisely those temperature conditions, which liquefy the protoplasm, 

 stimulate cell division, and those temperatures which coagulate 



1 Calkins, Arch. f. Entwickelungsmech., 1902, XV., p. 139. 



2 Greeley, Amer. Jour. Physiol., 1902, VI., p. 122. 



