Under normal conditions the functional excitation is at once followed by a succession of secondary processes, the “self-regulation of metabolism.” Self-regulation after a functional excitation is a fact demonstrated by experience. But in what manner does it take place in detail?
As the functional constituent members of metabolism involve a disintegration of the nitrogen-free atom groups, the functional self-regulation must necessarily furnish in sufficient quantity and in proper form the carbon, hydrogen and oxygen atoms, which have been removed in the production of carbon dioxide and water. This is accomplished, as is well known, by the food and the intake of oxygen. It is of importance to the maintenance of living substance that after every functional activity it is as soon as possible again capable of reaction. Therefore, it is absolutely necessary that this material is in the proper place, where building up is essential, and is at the same time constantly in proper form. Indeed, the restitution of the original state follows under favorable conditions with lightning rapidity, although varying in different forms of living substance. This occurs in the nerve in an extremely short time. From this it might be supposed that the living system by accumulating a store of the necessary compensation substances in suitable form, had made itself independent to a certain degree of the frequently varying supply of material obtained from the medium.
This may be held as the proper view, first with regard to compensation substances. The fact that living organisms can under some conditions remain for a lengthened period in a state of starvation, without losing their capability of activity, can only be explained by the presence of a great quantity of reserve supplies of compensation substances. In the course of work in the laboratory every physiologist has become acquainted with the fact that frogs which have been kept without food for a year, although much reduced in weight, are still capable of some muscular activity.
Fig. 12.
Motor ganglia cells from the spinal cord of the frog. A—In normal state. B—After an asphyxiation lasting 8 to 9 hours. (After Gordon Holmes.)
Fig. 13
Paramecium aurelia. A—In normal state. B—In a state of starvation.
Organs and tissue, which are cut off from all food supply through the blood and lymph, may remain active for many hours. H. v. Baeyer[64] has shown that the ganglion cells in the frog, in which saline solution was transfused at room temperature and containing no trace of organic substances and where irritability has been increased to the maximal by means of strychnine, were capable of strenuous work for nine or ten hours before losing responsivity. The nerves and muscles of the animal retain their excitability for even a longer period under the same conditions. Indeed, we have histological evidence of the existence of organic reserve material in the various cells in the form of embedded bodies in the protoplasm. As for instance the disappearance of the Nissl granules in the ganglion cells following great activity,[65] (Figure [12]), or that of the granules in infusoria cells during starvation.[66] (Figure [13].) We assume that a certain amount of organic foodstuffs in a state properly prepared is present in the cell. As the amount of these prepared substances is consumed, new quantities of stores, having undergone various preparatory processes, among which the enzymic actions may be considered to play a chief rôle, are brought into that form in which they appear suited to fill the gap produced by disintegration. Plant physiologists in particular have here again furnished us with some essential data for the assumption of the existence of such processes which regulate the transformation of reserve substances as well as its extent. Pfeffer[67] has found in several fungi and bacteria that there exists a compensation between the diastatic breaking down of the carbohydrates stored as reserve material and the quantity of dextrose introduced. He further found that the more the reserve substance is split up into dextrose the less of the latter is introduced from without and vice versa. De Bary[68] some time ago also observed in the bacillus amylobacter an analogous relation between the enzymatic cellular digestion and the quantity of dextrose introduced with the food. An equilibrium, therefore, exists between the required amount of dextrose and the extent of enzymic splitting up processes of the reserve material. A great number of similar processes have been observed. Even though the details of the whole preparatory assimilative processes are beyond our knowledge we can still say with certainty that, on the one hand, everywhere great quantities of organic reserve substances are always present in the cell, and on the other, that these substances are subjected to a transformation into suitable material for building-up processes, the extent of which is controlled according to need, by the processes of self-regulation.