1879.} 197 (Minot. 
formula, because each letter being a symbol for a factor that would 
otherwise be described by a whole sentence, the formula is much 
more concise and renders the relations of the factors evident at a 
glance, when the meaning of the symbols has been learnt. It shows 
that the weight of the body, leaving out of account the cells which 
die and fall off is determined by 
1, the number of cells. 
2, their average weight. 
The number of cells is determined by 
1, the ratio of multiplication; i.e., the number of cells pro- 
duced at each division. 
2, the frequency of the divisions, i.e., the rapidity with which 
the successive generations follow one another. 
Hence the weight is determined by — 
, the ratio of multiplication. 
, the frequency of division. 
3, the weight of the cells. 
4, the loss of cells. 
The fourth factor probably varies greatly in different individuals, 
even of the same species, and is partly if not mainly determined by 
external circumstances. The first factor is probably almost constant, 
and would therefore, if acting alone, cause the growth to be a geo- 
metrical progression, presupposing that the daughter-cells attain 
the parental size after each division. The ordinary method of the 
multiplication of cells is by division into two daughter-cells. In var- 
ious instances however the number of cells arising at once from the 
parent cell is much greater (large cells of medulla of bone, the 
Blutinseln, upper ends of the ovarian tubes of insects, etc.). But 
these exceptions are rare, and cannot result in any great departure 
from the average value of 2, for the number of cells produced at 
each division. It cannot be less than 2. The second factor is a 
function of senescence, and as far as I am aware has never before 
been alluded to. If its existence is as real as I believe, its import- 
ance is fundamental, and should be especially emphasized, because 
it introduces us to a peculiarity in the manifestations of vital activity, 
which has hitherto remained unnoticed. Senescence probably ex- 
hibits itself in other ways, in senile degeneration of the cells, but it 
need not be conceived as an active process, but is rather to be re- 
garded hypothetically as due to the gradual fading out of the impulse 
evolved at the moment of impregnation. We have no reason for 
no = 
