1879.] 191 [Minot. 
proportions of the cells; we are again baffled by the impossibility of 
determining this average. Moreover another point demands consid- 
eration, namely, that the number of cells united in the body of an 
animal at a given moment, when the size is to be measured, is less 
than the whole number of cells produced up to that time, because a 
variable number have died and fallen off. In man and many ani- 
mals the loss at one time is small — the epidermis, for instance, scales 
off gradually,—in forms which moult the loss at each moult is con- 
siderable, while in starfishes, for example, an accident may cause the 
loss of several arms, equal collectively to half or more than half of 
the total weight. In weighing, these losses are not taken into 
account. 
These considerations suffice, I think, to demonstrate that the 
weight of an animal is not an entirely accurate and satisfactory 
measure of growth, although practically it is our best standard. 
The weight of the body then represents the sum of the weights of 
the total number of cells united in one individual at a given time. 
In making this statement we assume that the intercellular substance 
is part of the single cells, an assumption which seems to me perfectly 
justifiable, as long as we maintain that the intercellular substance is 
generated by the cells. The weight then in short depends on: 1°, the 
number, 2°, the size of the cells—~two variables which are to be 
determined. 
In a previous paper! I endeavored to prove that all Metazoa (and 
probably all Protozoa) pass through successive cycles, each cycle 
beginning with the impregnated ovum, passing through youth to old 
age, and ending with death. Before death ensues, however, the 
sexual products are generated, and produce by their union a single 
cell, with which a new cycle begins. ‘This cell multiplies itself, and 
therewith growth is accomplished. Two fundamentally different 
processes here display themselves: the gradual senescence, which 
continually hinders and delays the multiplication of the cells, and 
their vital acts, at last suppressing them altogether at the moment of 
death; before senescence conquers, the sexual products are thrown 
off and effect the process of rejuvenation. The old cycle of cells 
passes away, but a new cycle is developed, a new egg-cell is produced, 
endowed with an extraordinary power of division. Evidently all the 
cells resulting from one impregnated egg belong in one cycle—a 
1 Recent Investigations of Embryologists. Proc. Bost. Soc. Nat. Hist., x1x 
(1877), 167. 
