98 METABOLISM AND NUTRITION 



which the greatest amount of work is done would be destroyed to the greatest 

 extent. But this is not true; on the contrary, these very organs seem to 

 suffer the least loss of substance, while the loss is greatest from those organs 

 upon which little or no demand is made in fasting. 



If this conception be correct and it must be admitted that direct observa- 

 tions are still very inadequate it would follow that in fasting the organs 

 do not do their work at the expense of their own substance. It seems that 

 all the organs contribute to the support of the body; but those organs which 

 are of primary importance for the maintenance of life, utilize the materials 

 thus contributed by all, in the performance of their particular functions ; that 

 is to say, they work at the expense of the less vital organs : their own state of 

 nutrition suffers less, and hence they decrease in weight relatively little. 



This view receives support from certain experimental facts. The bones, for 

 example, bear a part in the general levy made upon the organs. E. Voit fed 

 pigeons with food which was sufficient in every other respect, but was very poor 

 in calcium. The birds fared very well and were killed after some time. On 

 section it became evident that those bones which were used in the movements 

 of the animal were normal, while others such as the sternum and the skull were 

 brittle and in places were even perforated. Since calcium was being lost from 

 the body all the time, and none was being supplied in the food to replace it, 

 the " resting " bones gave up their calcium to the " active " bones. 



Probably a still more interesting example is furnished by Miescher's investi- 

 gations on the Rhine salmon. This fish leaves the sea in the best condition of 

 nourishment, but it remains in fresh water for six to nine months without eat- 

 ing anything. During this time it naturally becomes exceedingly thin and 

 gaunt, and its muscles greatly diminished in size; but the reproductive organs 

 become the more strongly developed. The substance of muscle has gone to make 

 ova and sperm cells. 



Sooner or later, however, there comes a time when the activity of the vital 

 organs and of those most necessary for the generation of heat in the body, 

 falls to the minimum. If animals be wrapped up in bedding they can be 

 kept alive for a brief time longer. But respiration and the heart beat soon 

 cease and the animal dies in a state of the .most profound exhaustion. 



4. INFLUENCE OF FOOD ON THE METABOLISM 



The most noteworthy thing about metabolism with food is the peculiar 

 position which proteid occupies with reference to the other organic foodstuffs. 

 If a dog be given a sufficient quantity of proteid with no fat or carbohydrate, 

 under proper circumstances the body will remain in an equilibrium of sub- 

 stance, the ingesta and the excreta completely balancing each other. If, how- 

 ever, the dog receive carbohydrate and fat in plentiful quantities but no pro- 

 teid, equilibrium never occurs. The body continually excretes nitrogenous 

 waste products which means that proteid is continually being destroyed 

 and after a time, which is somewhat longer than when no food at all is given, 

 the animal finally dies of " proteid starvation." 



Since we have no reason to suppose that there is any essential difference 

 between the chemical processes involved in the final decomposition of the food- 

 stuffs in the dog and in man, it is theoretically conceivable that a man also 



