A. W. GREELEY. 



they can be procured, and especially because their small size 

 makes it possible to study the structural changes in the living 

 protoplasm under high magnifications, which is out of the ques- 

 question in more bulky tissues. The protozoa were subjected 

 to thermal, chemical and electrical changes, and the structural 

 modifications produced by these means were studied. 



STRUCTURAL REACTIONS OF THE PROTOPLASM OF PROTOZOA TO 

 PHYSICAL AND CHEMICAL CHANGES. 



I. Reactions to Variations in the Temperature. 



In previous papers l I have described the structural changes 

 that occur in the protoplasm of various protozoa when exposed 

 to variations in the temperature, so that a very brief description 

 will suffice here. We find, exactly as in the case of organic col- 

 loids, that the fluidity of the protoplasm varies directly with the 

 temperature within certain limits. As the temperature is lowered 

 below the normal, 2OC., a very gradual coagulation occurs, be- 

 cause of the decrease in kinetic energy and consequent fusion of 

 the protoplasmic particles. This change is accompanied by a 

 loss of water, so that at o C. there is produced a nearly solid 

 opaque, spherical mass of protoplasm, which exists only in a rest- 

 ing condition. As the temperature is elevated above the normal, 

 the reverse changes occur through the increase in kinetic energy 

 acquired by the protoplasmic particles. They may be seen to 

 subdivide further and become more widely separated through 

 the absorption of water, so that the fluidity and motility of the 

 protoplasm is greatly increased. These changes continue until 

 the critical point is reached, at which coagulation suddenly 

 occurs, and the protoplasm goes into heat rigor, probably because 

 of some chemical change in the protoplasm itself. So closely 

 do these structural changes agree with those that occur in artifi- 

 cial colloids under the same conditions, that a description of one 

 would apply equally well for the other. Indeed, it was this 

 striking similarity between the results in the two cases, that led 

 me to compare the reactions of colloids and the protoplasm of 



1 Greeley, Amer. Jour. PhvsioL, 1901, VI., p. 201 ; BlOL. BULL., 1902, III., 

 p. 165 ; //>/,/., 1903, V.. p. 42. 



