Hyatt. 1 64 
[April s, 
eatnholic ditferoiitiatioii of the cell structure, and tliird the fissiou 
or division of tlie niotlier cell into dauglitor cells. Then this cycle 
repeats itself l>y the aid of nutrition and assimilation which furnish 
the materials for further anabolism and catabolism. 
The multiplication of cells of course adds to the number of 
nuclei and therefore adds to the sum of growth force in the body. 
In other words, each new nucleus is an additional center for the 
assimilation of food and storage of energy which is subsequently 
used in developmental catabolism leading to the formation of new 
centers of storage and distribution. But this increase as stated 
above is working at constantly increasing disadvantage owing to 
the still greater j>roportionate augmentation of the load, or in 
other words, of the products of the work done by the nuclei. 
Minot's researches and those of Maupas, as well as the general 
phenomena of old age, make it very probable that thei-e is also, 
in consequence of use and wear, either an absolute decline or 
decrement of force and mass in the nucleus itself taking place verj'^ 
gradually and visible externally only when it has become general 
and affects the existence of some function or occasions the decrease 
in size and loss of some organ or part, or the degeneration of the 
whole body in extreme cases of senility. 
If the nuclei were in constant ratio to the amount of c3^toj)lasm 
in the cell, there would be no optical confirmation of these remark- 
able observations. But Dr. Minot is able to add that the nuclei 
of cells present precisely the metabolic changes that one would 
expect to find in them if thejMvere centers of the assimilative and 
reproductive powers of the body. In the young cells of guinea 
pigs the nuclei are very large as compared with the surrounding- 
cytoplasm, and then diniinish with age in i)ro]»ortion to the mass of 
this cytoplasm. 
In Mau]>as's researches also the ultimate generations of the 
agamic cycle were found to pass through transformations in which 
they decreased in size, and the inicro-nuclei also degenerated and 
became unfit for conjugation. Thus, in spite of additions to the 
number of the colony caused by the multiplication of protozoans, 
the additions to the i)ower of growth as indicated by the size of the 
nuclei are proportionately on the decrease. There are of course 
other factors when the cells remain together and form a body as in 
Metazoa or a permanent colony as in some Protozoa. They 
necessarily become loaded by the dcA'^elopment of various kinds of 
