1862.] 121 



III. " Experiments on Food ; its Destination and Uses." By 

 WILLIAM S. SAVORY, Esq., F.R.S. Received May 1, 1862. 



(Abstract.) 



The experiments which are related in this paper refer to the des- 

 tination of food and its uses. 



Abundant, nay, superfluous evidence has been furnished to prove 

 that no one principle of food will alone suffice for nutrition ; but clear 

 and unequivocal evidence is still wanting to show how far each prin- 

 ciple of food is essential to life and health, provided all else save that 

 one be sufficiently supplied. This is a very different question. 



Again, ever since Liebig's famous classification of food into plastic 

 or nutritive and respiratory or calorifacient, some most important 

 questions in connexion with it have engaged the attention of physio- 

 logists. Amongst them are these : 



Is any food destined to the production of heat without being con- 

 cerned in the repair of the tissues that is, is any portion of the food 

 directly burnt in the blood ? 



Is any portion of albuminous food directly calorifacient, that is, 

 burnt in the blood without forming tissue ? 



This last question has more recently assumed another form, viz. 

 what is the source of urea ? Is it derived wholly from the metamor- 

 phosis of tissues, or directly to some extent from the blood ? In other 

 words, does any portion of nitrogenous food undergo a directly retro- 

 grade metamorphosis into urea, carbonic acid, and water ? 



The experiments were performed upon rats* and a hawk. The 

 animals were fed upon different diets, and the experiments may be 

 divided into three classes accordingly. In one class the diet was a 

 non-nitrogenous one, consisting of equal parts by weight of arrowroot, 

 sago, tapioca, lard, and suet ; for this mixture was found upon analysis 

 to yield only '22 per cent, of nitrogen. In another class the diet was 

 a nitrogenous one. It consisted of lean veal from which every visible 

 particle of fat had been carefully removed. This yielded upon ana- 

 lysis only 1*55 per cent, of fat. In the third class the diet was a 

 mixed one. It consisted of a combination of the two former diets. 



* Rats were chosen as subjects for these experiments because they are omnivo- 

 rous and will readily feed on almost any kind of diet. Moreover from their size 

 they are very convenient to manage. 



