430 NUTRITION. 



that the proportions in which these factors of nutrition are mixed 

 in the food exert the most decided influence on the welfare of the 

 organism, and that the intermixture of the different factors of 

 nutrition is essential for the metamorphosis of matter. Great as 

 are the fluctuations which nature allows in these proportions, an 

 undue preponderance of one or other of the factors always acts 

 injuriously upon the due course of the process of nutrition : no 

 single section of this process can go on without the concurrence of 

 all these factors ; thus, for instance, all these experiments teach us 

 that the carbo-hydrates alone are not sufficient for the formation of 

 fat in the animal body ; in order that fat may be formed, protein- 

 bodies as well as salts must co-operate in the metamorphosis ; and 

 it is only by the mutual action of these substances that a formation 

 of fat can possibly take place. Had the results of the above- 

 described experiments been duly considered, such a series of obser- 

 vations as that instituted by Letellier,* who fed turtle-doves on 

 sugar, would hardly have been necessary. Letellier having deter- 

 mined the quantity of fat in doves of equal age, weight, &c., fed 

 similar animals for a long time with sugar ; the birds, several of 

 which died after eight days, lost on an average 5*1 grammes, or 

 3'4# of their bodily weight daily ; when a little pure albumen was 

 added to the sugar as food, they died at a somewhat later date, 

 having lost daily 2'3 grammes, or 1'53 of their weight. While 

 the amount of fat in the healthy birds before the commencement 

 of the experiments was 20*88 grammes, or 15-J, the amount after 

 death, in those which had been fed on pure sugar, was only 11*3 

 grammes or 7'36f , and in the case of those which had simultane- 

 ously received albumen (and when life was therefore somewhat 

 prolonged) it was only 1*57 grammes or 3'15. Indeed even after 

 feeding them with butter, the birds sunk, and there was a consi- 

 derable loss not only in their bodily weight, but even in their fat. 

 (The daily loss of bodily weight was 3 '25 grammes or 2*82~, and 

 altogether more than half the original quantity of fat disappeared, 

 there being only 7 after death.) The animals, therefore, sunk in 

 this, as in the other cases, with all the symptoms of inanition, while 

 the process, whose most essential requirements were present, not 

 only failed, but could scarcely be said to have commenced. Hence 

 this proposition, which we previously regarded as resting on many 

 inferences, may be considered to be definitely proved by these 

 experiments. 



This consideration directly leads us to the quantitative relations 

 * Ann. de Cliim. et de Phys. T. 11, p. 433. 



