332 PHYSIOLOGIC-U. EEGTLATIOXS 



of it and slower of others. Hence recovery of total substance 

 depends on what particular materials are ingested. In a mixture, 

 water is eliminated most rapidly when in a certain excess relative 

 to other materials ; nitrogen next, chloride next, and carbon last. 

 Other substances could be intercalated in this list. Each compo- 

 nent has a velocity quotient characteristic of it, and these quotients 

 may be investigated either in ingestions of more or less pure com- 

 ponents, or in mixtures. In general, also, diverse quotients are 

 found for one component with each mixture, and this is a matter 

 for further study. 



It is a plain fact that every organism tends to have a constant 

 amount of material in it. In some protozoa accession of material 

 leads to reproduction of more individuals (Adolph, '31a), restoring 

 each to a size near the mode. In mammals, accession leads to faster 

 disposal, at rates differing for each constituent (energy, carbon, 

 nitrogen, water). Deprivation of material leads to extraordinary 

 efforts to obtain it, and especially to obtain the very constituents 

 that are lacking. TThereas the human individual sometimes relies 

 upon the bath-room scales to guide his rate of intake, organisms 

 generally temper their exchanges so as to maintain a uniform body 

 weight without any visible measuring device. 



§ 119. Glucose ix dog 



One of the first components for which a maintenance of con- 

 stancy was realized to exist (Bernard, 1855; Chauveau, 1S56) was 

 sugar. Deprivation of carbohydrate did not much decrease the 

 blood's concentration of sugar; feeding nothing but sugar, even 

 infusing a solution of it, did not much increase it. The identifica- 

 tion of glycogen as one of the forms of storage for carbohydrate 

 led to the dim realization that reversible equilibria buffer the 

 changes in actual glucose content of the body. From this prototype 

 of reactions through which excesses and deficits tend to be ab- 

 sorbed, has grown the knowledge of diverse paths of disposal for 

 sugars, as well as for innumerable other components both chemical 

 and physical. 



To obtain quantitative data upon unanesthetized dog, two types 

 of glucose increment are used; excesses are produced by continuous 

 intravenous infusion of glucose, deficits by previous intravenous 

 injection of insulin. The glucose content of the body as a whole is 

 computed on the assumption that the volume of distribution of glu- 



