IIYDROCARBONACEOUS SUBSTANCES. 69 



were then kept upon a definite regimen, in which the quantity of fat was 

 determined by analysis. This was continued for periods varying from 

 one to eight months, after which the animals were killed and their 

 tissues examined. The result showed that considerably more fat had 

 accumulated in the system than had been supplied in the food. Conse- 

 quently, oleaginous substances must in some cases, and perhaps habitu- 

 ally, be formed in the interior of the body by transformation of other 

 nutritive materials. There is no discrepancy among observers on this 

 point. 



As for the special materials from which fat is thus produced in the 

 animal system, its most probable source seems to be the carbo-hydrates. 

 It has already been shown (page 63,) that such a change undoubtedly 

 takes place in vegetables ; and as it is not effected in plants, so far as 

 we can judge, by simple deoxidation, but by a kind of process which 

 may also take place in animals, there is no reason for doubting the 

 possibility of a similar transformation in the interior of the animal 

 body. Other considerations make it highly probable or certain. Vege- 

 table-feeding animals, like sheep and cows, living on green food abound- 

 ing in carbo-hydrates, will often accumulate a large amount of fatty 

 matter in the system, or discharge it with the milk. In many of the 

 experiments just quoted, the carbo-hydrates preponderated so much in 

 the food supplied, that the excess of fat produced during the observa- 

 tion could hardly be attributed to any other source. And finally, it is a 

 matter of common experience that food consisting of starchy and sac- 

 charine materials is especially a fattening food, both for the domestic 

 animals and for man. 



But these substances do not possess in themselves the requisite con- 

 ditions for a fatty transformation ; it can take place only in the living 

 body. As the deoxidation of carbonic acid and water by plants is 

 effected under the influence of their chlorophylle, so the carbo-hydrates 

 of the food require the action of the animal tissues for their conversion 

 into fat. This explains why the fat production varies so much under 

 the same diet in different animals, and even in different individuals of 

 the human species. There are cases of hereditary obesity, coming on 

 at the same period of life in the children as in the parents, irrespective 

 in great measure of the kind of food employed ; and there are persons 

 who seem hardly capable of taking starchy or saccharine substances 

 without converting them into fat, while others may continue a mixed 

 diet indefinitely without increasing their adipose tissue. 



It is not unlikely that fat may also be formed from the albuminous 

 matters of the food, though the evidence of this is less satisfactory than 

 in the case of the carbo-hydrates. Carnivorous animals, as a rule, have 

 less fat than the herbivora ; and, among men, those who habitually con- 

 sume a large proportion of meat are less liable to obesity than those 

 living mainly on vegetable food. Nevertheless, it is believed by many 

 that fat is sometimes the result of a partial decomposition of albu- 

 minous matters. In this case, the production of fat must be accom- 



