334 STUDIES IN GENERAL PHYSIOLOGY 
cell-membrane, and that it certainly has no relation to the 
orientation of the first cleavage plane. For when we first 
allow the eggs to develop in ordinary sea-water into the two- 
cell stage before bringing them into dilute sea-water, it can 
be noticed that the first cleavage plane may lie in any posi- 
tion with regard to the point of rup- 
ture; the material lying nearest the 
rupture will be that which flows out. 
Figs. 91-94 are drawings of eggs 
the membranes of which were made 
to rupture in the two-cell stage, and 
which illustrate what has been said 
more clearly than words. Since the 
extraovate develops in all cases, if it is only sufficiently large, 
we must conclude that, so far as the question of divisibility 
is concerned, the protoplasm must be considered an isotropic 
substance. 
9. What conceptions can we form of the nature of the 
smallest elements of living matter which are capable of 
development? As Nussbaum has shown, every attempt that 
has been made of assuming as the ulti- 
FIG. 91 
mate elements of living matter some- 
thing analogous to the atom and the 
molecule has failed, for the simple rea- 
son that two different substances, nucleus 
and protoplasm, are necessary. One 
might assume that a combination of two 
different ‘‘micelle’’—one composed of 
nuclear material, the other of proto- FIG. 92 
plasm—might represent the smallest living element. Our 
experiments show that such an idea would be entirely wrong, 
when full capacity for development is taken as the criterion 
of living matter, inasmuch as a very considerable quantity 
of substance is necessary for full development—an amount 
Digitized by Microsoft® 
