CELL SIZE AND NUCLEAR SIZE yf 
of Warburg. I find that the chromosomal mass grows at the 
rate of 8 per cent for each division up to the 32-cell stage. It is 
difficult to connect this rate of growth of the chromosomes with 
the lack of growth in the nucleinic acid content as shown by Mas- 
ing, or with the lack of growth of the nuclein content as shown by 
Shackell, and it seems necessary to assume as both of these in- 
vestigators have done, that these substances are already pre- 
formed in the protoplasm. If this be true, I venture the sug- 
gestion that the large amount of chromatin (oxychromatin) 
which escapes into the cell body when the germinal vesicle dis- 
solves may constitute the nuclein and nucleinic acid which is 
distributed through the cell body. 
VII. Senescence, reyuvenescence, and the ratio of nucleus to plasma. 
It is well known that Minot (90, ’95, ’08) maintains that the 
cause of senescence is the increase of plasma and its products at 
a rate greater than that of the nucleus. According to his view 
the egg at the beginning of development is in a senile condition, 
‘‘in which there is an excessive amount of protoplasm in propor- 
tion to the nucleus, and in order to get anything which is young 
a process of rejuvenation is necessary’ . . . . During the 
segmentation of the ovum the condition of things has been re- 
versed so far as the proportions of nucleus and protoplasm are 
concerned. We have nucleus produced, so to speak, to excess. 
The nuclear substance is increased during the first phase of de- 
velopment. Hence our conclusion:—Rejuvenation is accom- 
plished chiefly by the segmentation of the ovum.”” He sums up 
his views on this subject in his four laws of age (08, p. 250), the 
first two of which are: 1. ‘‘Rejuvenation depends on the in- 
crease of the nuclei. 2. Senescence depends on the increase of 
the protoplasm, and on the differentiation of the cells.” 
Richard Hertwig’s views (’89, ’03, ’08) are apparently diamet- 
rically opposed to those of Minot, though I do not find them so 
definitely expressed. He finds that senescence, or rather ‘de- 
pression’ and ‘physiological degeneration,’ are accompanied by 
an enormous growth of the nucleus. As a result of his work on 
