METABOLIC RATE AND PARTITION OF NUTRIENTS 501 



It will be observed that those organs which are most essential to the 

 preservation of existence are those which suffer least extensively from 

 the unbalanced tissue-degradation which results from the fall of the 

 Nutrient-level consequent upon deprivation of food. This must be due 

 to some definite peculiarity of the metabolism of those tissues which 

 so especially maintain their weight under these adverse circumstances. 

 The nature of this peculiarity may be inferred from the fact that the 

 speed of metabolism is exceptionally great in just those tissues, the 

 Heart and Nervous System, which most successfully resist the disinte- 

 gration-effects of inanition. Thus the heart is constantly transforming 

 large amounts of potential energy into mechanical work, the mainte- 

 nance of life in the higher Metazoa depends in fact upon its doing so, 

 and yet it carries within itself an extraordinarily small reserve of 

 energy-yielding materials. The Glycogen-content of the muscular 

 tissues of the heart, instead of being exceptionally high, is, as a matter 

 of fact, exceptionally low. The heart must thus depend for the 

 maintenance of its exertions upon the direct and constant withdrawal 

 of nutrient materials from the circulating fluids. In so doing it is 

 forced to compete with all the other tissues of the body and yet it does 

 so with so much success that whereas the majority of the other tissues 

 lose a very considerable part of their weight, the heart maintains the 

 integrity of its substance until death is imminent. This implies that 

 the rate of utilization of nutrients by the heart must greatly exceed 

 that of the other tissues, so that the foodstuffs are appropriated in 

 advance of the ability of other tissues to do so. 



The high Metabolic Rate of the central nervous system may be inferred 

 from the fact that its consumption of oxygen is exceptionally great. 

 The first effect of deprivation of oxygen is to arrest the higher activities 

 of the central nervous system and those substances which paralyze 

 the oxidizing enzymes, such as the Cyanides, arrest the activities of the 

 central nervous system before any other tissue is affected to a com- 

 parable degree. The intensity of Oxidations in the central nervous 

 system testifies to the rapidity of the destruction of its constituents. 

 The fact that it maintains its integrity even in starvation, therefore, 

 implies a proportionate rapidity of reconstruction. 



The synthesis of the various tissues of the body from the foodstuffs 

 which are contained in the circulating fluids may be regarded as a 

 multitude of parallel reactions, all consuming similar substrates 

 although not in identical amounts and proportions. Now in any group 

 of Parallel Reactions, that is, of reactions which are occurring simul- 

 taneously and consuming the same raw materials, each substrate which 

 enters into the reactions is shared between them in proportion to the 

 velocity with which they occur. The various reactions proceed at their 

 own independent rates and if the quantity of materials available for 

 transformation were unlimited, each reaction, or the synthesis of each 

 particular kind and type of tissue, would go forward at the same speed 

 as it would if the other tissue-syntheses were not occurring simul- 



