THE MECHANISM OF LIFE 489 



to 1, i.e., metabolic equilibrium continues to exist in spite of the 

 absolute change in the extent of metabolism. Hering very 

 fittingly terms this maintenance of equilibrium " the internal self- 

 regulation of the metabolism of living substance." Such a self- 

 regulation of metabolism within definite limits is realised in man 

 in the behaviour of the body toward ingested nitrogen. With 

 a definite quantity of ingested proteid, which Yoit has found to be 

 ajjproximately 118 gr. in the labouring man, nitrogenous equili- 

 brium continues to be maintained ; i.e., the more nitrogen is 

 introduced in the proteid, the more is excreted in the urine, a sign 

 that the dissimilation of proteid increases in the same proportion 

 as the assimilation. 



This last example leads us to the action of stimuli upon biotonus, 

 and we must consider this in some detail. 



B. THE ACTION OF STIMULI UPOX THE JIETABOLISM OF BIOGENS 



1. Changes of Biotonus upon Total Stimidation 



It has been seen that biogens are very labile compounds con- 

 taining much intramolecular heat ; in other words, the atoms of 

 their molecules are in active vibration. As a result of this, certain 

 atoms come occasionally into the sphere of attraction of others, 

 and becoming united with them into a more fixed combination, 

 separate off as an independent molecule. In this way the spon- 

 taneous dissimilation of the biogen molecule results. But the 

 chemical affinities m.ade available by the withdrawal of the separated 

 groups of atoms have in the constituents of the food that is 

 taken in and transforjned in manifold ways, an opportune possibility 

 of combining again, so that the residue of the biogen can be rebuilt 

 into a whole biogen molecule. Thus spontaneous assimilation of 

 the biogen molecule follows its spontaneous dissimilation. 



Since the dissimilation of the biogens is conditioned by the 

 intramolecular vibrations of the atoms, it is evident that all factors 

 that increase such vibrations must assist the process of dissimila- 

 tion. In this way is explained the increased decomposition of 

 living substance that can take place under the influence of 

 chemical, mechanical, thermal, photic, and galvanic stimuli. If the 

 external influences are so strong that a profound decomposition of 

 the molecule takes place, and no residue capable of icgeneration is 

 left, there results a decrease of the living substance, and with ovei'- 

 stimulation death. On the other hand, the process of dissimilation 

 is depressed by all factors that diminish the intramolecular vibra- 

 tions of the atoms in the biogen molecule, such as cooling and the 

 action of substances that fixate single atoms in a definite position 

 by chemical attraction. All of thesr stimuli that either excite 



