386 VETERINARY PHYSIOLOGY 



different from those of the body leads to their appearance in 

 those tissues. 



Fats are also formed from the carbohydrates of the food. 

 Feeding experiments upon pigs and other animals, carried out 

 in this country by Laws and Gilbert, 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 protein of the food eaten. 

 It must therefore have been formed from the carbohydrates. 



The evidence that fats may be formed from the proteins 

 of the food is conflicting. In the ripening of cheese it is 

 undoubted that under the influence of micro-organism proteins 

 are changed to fats, and in all probability the same thing 

 occurs in the formation of the fatty adipocere in the muscles of 

 the dead body during putrefaction. At one time it was 

 supposed that under the influence of such poisons as phosphorus 

 the proteins of the cells of the mammalian tissues are changed 

 to fat. But careful chemical examination has shown that the 

 so-called fatty degeneration is due to accumulation of already 

 existing fats in the affected organs. Voit fed dogs on lean 

 beef, and found that, while all the nitrogen was discharged 

 from the body, the carbon was retained, and he concluded 

 that it was retained as fat. But he failed to recognise that 

 even lean flesh contains both fat and glycogen from which 

 the fat can be formed. At present we have no direct evidence 

 that the fats of the body are formed from proteins. 



2. In the Liver. The liver is a storehouse of carbohydrates 

 and fats (p. 387). Lecithin is always present in the liver, even 

 in prolonged fasting. 



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

 within their muscle fibres ; but in mammals such a storage is 

 limited in amount. 



B. Proteins may, to a small extent, be stored in muscle, 

 especially after a fast or a prolonged illness. But in the healthy 

 mammal it is difficult to get such a storage, except in athletic 



