426 Louise Hoyt Gregory 



ceases there is an excess of nuclear material, and the protoplasm 

 then begins to grow and to become differentiated. This is sen- 

 escence, which, according to Minot, begins in the two-cell stage. 

 In other words, rejuvenation implies the increase of nuclear mate- 

 rial, senescence the increase of protoplasmic material, both proc- 

 esses being due to changes in the size relations of nucleus and 

 cytoplasm. These processes take place especially in the growth 

 and development of the Metazoa. He has little faith in the view 

 that these same processes take place in the Protozoa, and does not 

 accept as final the results of Maupas and Calkins on the degener- 

 ation of the protoplasm and the appearance of old age in the life 

 cycle of a protozoan individual. Begging the question, he de- 

 mands proof of an excess of protoplasmic material in the cells 

 which are in a condition of lowered vitality before he will accept 

 the view of senescence in Protozoa. Hertwig, on the other hand, 

 would have an excess of nuclear material in the cells in a weakened 

 condition. Both investigators are concerned with size relations 

 only, and have failed to recognize the importance of the constant 

 changes taking place in the quality of the nuclear and protoplas- 

 mic material. There is certainly a possibility, if not a probability, 

 that they both have confused effect with cause. 



In the ordinary metabolic processes of digestion, assimilation, 

 etc., physiological changes are constantly taking place which affect 

 the nature of the nucleus and cytoplasm. If these processes are 

 disturbed in any way, there is, as a result, a detrimental effect 

 upon the character of the protoplasm, and certain morphological 

 changes set in. Calkins has shown that at certain periods in the 

 history of Paramecium, the activities connected with the ordinary 

 digestive functions of the cell were affected, and as a result, the 

 macro-nucleus became more dense, and the endoplasm crowded 

 with undigested food particles. This condition would end in 

 physiological death unless salts were given which would stimulate 

 the processes of digestion and enable the cell to resume the normal 

 conditions of growth and division. Again, at a later period, a 

 more serious depression occurred, in which the ordinary digestive 

 functions were not affected, the endoplasm and macro-nucleus 

 being normal, on the other hand the cortical plasm and the micro- 



