EXCHANGE OF MATERIAL.. 443 



The quantity of water and mineral bodies void eel with the urine 

 and faeces can easily be determined. The quantity of water elimi- 

 nated by the skin and lungs may be directly determined by means 

 of PETTENROFER'S apparatus. The quantity of oxygen taken up is 

 calculated as the difference between the weight of the individual 

 before the experiment plus all the directly-determined substances 

 taken in, and the final weight of the individual plus all his excreta. 



I. Exchange of Material in Starvation. 



In starvation the decomposition in the body continues uninter- 

 ruptedly, though with decreased intensity; but as it takes place at 

 the expense of the substance of the body, it can only continue for a 

 limited time. When an animal has lost a certain fraction of the mass 

 of the body death is the result. This fraction varies with the condi- 

 tion of the body at the beginning of the starvation period. Fat ani- 

 mals succumb when the weight of the body has sunk to J of the orig- 

 inal weight. Otherwise, according to CHOSSAT, animals die as a rule 

 when the weight of the body has sunk to f of the original weight. 

 The period when death occurs from starvation not only varies with 

 the different nutritive condition at the beginning of starvation, but 

 also with the more or less active exchange of material. This is more 

 active in small and young animals than in large and older ones, but 

 different classes of animals show an unequal activity. Children 

 succumb in starvation in three to five days after having lost J of 

 their bodily mass. Grown persons, according to ordinary state- 

 ments, can live for three weeks if they have water ; we also have 

 statements of much longer periods of starvation. For instance, a 

 person suffering from melancholia, who drank water but took no 

 food, died after 41 days, and the Italian MERLATTI withstood a 

 starvation period of 50 days, during which it is stated he only took 

 water. - Dogs can live without food from four to eight weeks, birds 

 five to twenty days, snakes more than half a year, and frogs more 

 than a year. 



In starvation the weight of the body decreases. The loss of 

 weight is greatest in the first few days, and then decreases rather 

 uniformly. In small animals the absolute loss of weight per day is 

 naturally smaller than in larger animals. The relative loss of weight, 



