THE FOOD AND DIGESTION 365 



that heat elimination is diminished, and the temperature is 

 raised in fevers. 



It is not necessary to assume that there is a special heat 

 regulating nervous mechanism, since the nervous arrange- 

 ments presiding over the vessels and glands of the skin are 

 capable of immediately responding to change of condition 

 calling for their intervention. 



II. STOKAGE OF SURPLUS FOOD. 



This storage takes place chiefly in three situations : (1) 

 Fatty tissue ; (2) muscle ; (3) liver. 



1. In Fatty Tissues. In most mammals the chief storage 

 of surplus food is in the fatty tissues. 



(1) That the fat of the food can be stored in them is 

 shown by the fact that the administration of large amounts 

 of fats different from those of the body leads to their appear- 

 ance in those tissues. 



(2) Fats are also formed from the carbohydrates of the 

 food. Feeding experiments upon pigs and other animals 

 have definitely proved that sugary foods are changed to fat 

 in the body and stored in that form. The following may be 

 given as an example of such experiments. Two young pigs 

 of a litter were taken, and one was killed and analysed. The 

 other was fed for weeks on maize, the amount eaten being 

 weighed and the excretion of nitrogen by the pig being 

 determined. The animal was then killed and analysed, and 

 it was found that the fat gained was more than could be 

 produced from the fat and proteid of the food eaten. It must 

 therefore have been formed from the carbohydrates. 



(3) There is good evidence that in excessive proteid feed- 

 ing the non-nitrogenous part of the proteid molecule may be 

 stored as fat, at least in carnivorous animals. Thus, a dog 

 fed on lean meat does not lose all his fat. It has recently 

 been maintained that the evidence in favour of the formation 

 of fats directly from proteids is unsatisfactory ; but since 

 proteids yield carbohydrates, and since carbohydrates form 

 fats, it must be admitted that proteids may be a source 

 of fats. 



2. In Muscle. Some animals, as the salmon, store fats 



