1914] Longevity of Insects 335 
differentiation, he claims, is irreversible. He therefore makes 
no provision for rejuvenation in the Metazoa. C. M. Child 
(10) has recently constructed a theory, which I will describe 
shortly, based on certain experiments and upon our present 
knowledge of the cell activities. 
Cells go through two processes—one constructive and bene- 
ficial or life-giving, i. e. metabolism—the other destructive, 
katabolism. Both are necessary to life and a balance is main- 
tained between them—when however, this equilibrium is upset 
in the direction of the katabolic processes, senescence is the 
result and finally death. The true measure of senescence then, 
may be taken to be inversely the rate of metabolism. 
In the life processes, many compounds are formed which 
cannot be made in the laboratory without the use of great heat 
or chemicals which are incompatible with life. It is believed 
more and more generally that a study of the physical conditions 
of the life substance, protoplasm, would throw great light on 
these processes. Alsberg in his recent paper (2) on the mechan- 
ism of cell activities, has given a resumé of present day knowl- 
edge and conjecture on the subject. 
The nature of protoplasm has been found to be similar to 
that of colloidal solutions and to emulsions. It is made up of 
substances that tend to concentrate at surfaces—this concen- 
tration and reduction of the size of the phase results in an 
enormous surface energy, which increases in immense propor- 
tion to the smallness or roundness of the surface of that phase 
or chemical locality. The very general composition of proto- 
plasm, i. e., 80% water, 15-20% solid and 5% fats, would make 
its rigidity impossible were it not for some emulsified condition. 
It being a well known fact that emulsions often show great 
rigidity. 
Since these substances have a tendency to form phases or 
localizations of chemico-physical conditions and since all these 
phases are in contact and all differ more or less in permeability, 
it is very possible that they act as a long series of interacting 
yet separate, semi-porous test tubes. A reaction may go toa 
certain stage then penetrate into the next phase and while 
being isolated and going through another reaction, may still 
influence the first phase—thus making it possible to complete 
a very complicated and apparently impossible chemical change. 
