RESPIRATION 301 
molecule of protoplasm apparently does not enter, can 
only go on in the living cell. Other similar instances could 
be quoted. 
The probable course of events in respiration is that the 
oxygen in some way unites with the protoplasm, rendering 
it unstable, and initiating a series of decompositions which 
result in the successive formation of many bodies of less 
complex composition, each successive decomposition pro- 
ducing simpler ones, till finally carbon dioxide and water are 
formed. Simultaneously, reconstruction of the protoplasm 
goes on, many of these residues, instead of being at once 
decomposed, being in whole or in great part, together with 
new material supplied to it in the shape of food, built up 
again into its substance, and again broken down in further 
decompositions. If the temperature is low, the breaking 
down of the protoplasm proceeds but slowly, and recon- 
struction is rapid, so that under these conditions the quantity 
of oxygen absorbed or fixed as intramolecular oxygen by 
the protoplasm is greater than the quantity of carbon dioxide 
formed by its decomposition. At a higher temperature 
decomposition is much more easily carried on, and its 
products are more numerous and simpler. The decom- 
position and recomposition go on side by side, simpler bodies 
being gradually produced, either by their splitting from the 
protoplasm directly, or by their being formed at the expense 
of the more complex decomposition-products during processes 
of slow oxidation in the substance of the protoplasm, till 
finally a certain production of carbon dioxide and water is 
arrived at. So long as the protoplasm remains alive the 
amount of these is relatively small, reconstruction con- 
tinually taking place. When, however, the protoplasm 
dies, simple bodies, such as carbon dioxide, water, and 
possibly ammonia, in addition, are produced abundantly 
from the decomposition which attends its death. 
If the auto-decomposition of protoplasm during life 
involved such a splitting-up as would lead to the formation 
of nothing but these, nearly all the potential energy of the 
