THE GENERAL CONDITIONS OF LIFE 275 



organism have been obtained in the case of men only. Voit ('81) 

 has shown that an adult man performing active work can subsist 

 upon a daily food comprising 118 grs. of proteid, 56 grs. of fat and 

 500 grs. of carbohydrate. With such a diet the man is in 

 metabolic equilibrium, i.e., the quantities of elements excreted in 

 the urine, the sweat, the expired- air, and the faeces are equal to 

 those that are introduced with the food. But, more specifically, 

 these values for the individual elements, such as nitrogen, carbon, 

 etc., introduced with the food must be determined separately, since 

 the body when, e.g., in carbon equilibrium is not necessarily always 

 in nitrogen eqidlibrium. It is thus found that nitrogen 

 equilibrium can be obtained with a quantity of proteid of only 50 

 grs. (which corresponds to 7*5 grs. of nitrogen), provided only that 

 the quantity of the non-nitrogenous food-stuffs, carbohydrates and 

 fats, is correspondingly increased. 7 '5 grs., therefore, would 

 correspond to the daily minimum of nitrogen with which a man 

 can continue to exist. 



The minimum of food necessary to the maintenance of meta- 

 bolic equilibrium and life is of great importance. If the income 

 of food rises above the minimum, metabolic equilibrium is 

 disturbed only in a very slight degree, slightly smaller quantities 

 of elements appearing in the excreta than are taken in with the 

 food. These very small quantities remain in the body and serve 

 for the increase of living substance and the storing up of reserve - 

 substances, a phenomenon that in husbandry is termed fattening. 

 But this depends upon many factors, which are as yet known 

 exactly only in part. If, on the other hand, the quantity of food 

 falls below the minimum or becomes zero, the condition of hunger 

 or inanition appears, in which the metabolic equilibrium becomes 

 more and more disturbed. This condition has been investigated 

 more fully. 



It is worth while to follow somewhat fully the changes 

 experienced by the living organism in the condition of inanition. 

 Every living cell under normal conditions possesses within itself in 

 greater or less quantity substances at whose expense the vital pro- 

 cess continues for a time if the food-supply be cut off. These are 

 its reserve-substances. It is a general fact that during inanition the 

 reserve-substances disappear first. Plant-cells that are filled with 

 starch grains consume these when they are brought into the dark, 

 i.e., when they are forced to hunger, for in the dark no assimilation 

 of starch from carbonic acid and water, in other words, no nutri- 

 tion, takes place. Infusoria, whose cell-bodies in their infusions, 

 where they revel in a superfluity of food, contain all sorts of 

 particles, and hence appear opaque and granular, become clear, 

 transparent and free from granules, when placed in water 

 containing little food-stuff; their cell-bodies become gradually 

 smaller (Fig. 125). The cell, therefore, does not die immediately 



T 2 



