PHASES IN THE LIFE OF THE INDIVIDUAL 677 



also tend to disappear. Hodge 1 has made a comparison of the 

 changes in the cells of the first cervical ganglion with the follow- 

 ing result : 



Nucleoli observable 



Volume of Nucleus. in Nucleus. 



At birth . . 100 per cent. In 53 per cent. 



At 92 years . . 64'2 5 



Thus the nucleoli are often apparently quite absent in extreme 

 old age. The nuclei, besides becoming smaller, grow irregular 



FIG. 151. Group of nerve cells from the first cervical ganglion of a child 

 at birth. (After Hodge, from Minot's Age, Growth, and Death, 

 G. S. Putnam & Sons, and John Murray.) 



in shape, and in the cytoplasm there is a deposition of pigment 

 granules. 



Senescence in men is said to commence at about the age of 

 fifty, 2 but it is obvious that no definite limit can be assigned 

 to the period, since in some of the organs changes which are in 

 their nature degenerative begin quite early in life. 



Spermatozoa continue to be produced even in quite ad- 

 vanced old age, and instances have been recorded of men of 



1 Hodge, "Die Nervenzelle bei der Geburt und beim Tode an Alter- 

 schwache," Anal. Anz., vol. ix., 1894. 

 18 Lee, loc. cit. 



