In the animal body, however, there is no such accumulation of decomposition products as is implied here, but the principle involved may possibly admit of application.
It is generally understood that muscular energy comes primarily from the decomposition or oxidation of non-nitrogenous material, either of the food or of the tissues; and in man we are accustomed to measure the amount of muscular work performed by the amount of oxygen consumed and the amount of carbon dioxide thrown out. In other words, the potential energy of the foodstuffs is made available through oxidation. This, however, is not always the case. Thus, in Ascaris, a round worm inhabiting the intestine of some of the higher animals, we have an animal that can live and show extremely active movements for days at a time without any appreciable amount of oxygen. Carbon dioxide is given off abundantly, however, thereby implying a cleavage or process of disintegration in which energy is freely liberated for the necessities of the animal's machinery. It is quite apparent, however, that oxidation is not the source of muscular energy in these organisms. It may be claimed, and perhaps justly, that such an illustration as this can not be applied legitimately to animals higher in the scale of life, yet there is experimental evidence from various sources pointing in the same direction. Thus, Stoklasa has shown that organs from the higher animals, notably the lungs, liver, pancreas and muscle, yield on pressure fluids, from which by precipitation with alcohol and ether enzymes can be separated, having the power of producing in perfectly sterile solutions of sugar—and with exclusion of micro-organisms—alcoholic fermentation. The proportion of carbon dioxide and alcohol formed under these conditions is the same as produced by yeast. Remembering that in alcoholic fermentation sugar is simply split apart into alcohol and carbon dioxide, it is readily seen that the liberation of a certain amount of energy is possible by simple cleavage of the sugar molecule and without the intervention of oxygen. This then is a form of anaerobic metabolism or respiration, possibly analogous to that which occurs in Ascaris, where carbohydrates are broken down and energy set free for the needs of the organism. Again, Hermann years ago proved that a freshly excised muscle, from which all free oxygen had been separated by exposure to a vacuum, when placed in an oxygen-free medium could be made to work and give off carbon dioxide. Other data of a similar nature might be presented showing quite conclusively the power of animal tissues to carry on various decompositions of complex organic matter with an output of carbon dioxide and with consequent liberation of energy where free oxygen is entirely wanting. These are facts, however, well known to physiologists, but they serve to emphasize the validity of the present
- Zentralblatt für Physiologie, Band 17, p. 465.