CHAPTER IV. 



THE FATS. 



THE origin of fats in the animal body is threefold : one portion is 

 derived from the fats which have been ingested as food ; another 

 portion is formed from the carbohydrates ; while a third portion 

 results from the decomposition of albumins. As food-stuffs the fats 

 are of great importance, because their caloric value is quite high 

 higher in fact than that of the carbohydrates and albumins ; but, 

 like the carbohydrates, they are unable to take the place of the 

 albumins. Animals that are fed exclusively on fats die sooner or 

 later, although they may become quite fat during the period of their 

 special diet. In the animal body they represent a variable amount 

 of reserve food, which is conveniently stored in the subcutaneous 

 areolar tissue, in the omentum and mesentery, in the bone-marrow, 

 etc. In case of inanition it is utilized long before the tissues of the 

 body proper are attacked, and we accordingly find that in persons 

 who have died from wasting diseases every vestige of fat may have 

 disappeared, while the muscular nutrition may still be fair. 



That portion of the body fat which is derived from the fats 

 ingested as such is really the smallest portion, and by far the greater 

 amount results from the carbohydrates. The manner in which this 

 transformation takes place is unknown, but it is probable that the 

 carbohydrates which are utilized for this purpose are first decom- 

 posed, and then reduced ; and that the fats finally result through 

 a synthesis of such reduction-products. Such syntheses, however, 

 cannot at once be compared to those which take place in plants, for 

 here we have seen that the fats can be formed directly from water 

 and carbon dioxide. In animals this does not occur, and we can 

 definitely state that if the fats are formed in the manner indicated 

 at all, they result from very much more complex molecules. 



The origin of the fats from carbohydrates can be demonstrated in 

 various ways. Dumas and W. Milne Edwards have shown that 

 bees which are fed exclusively on sugar produce three times as much 

 wax as compared with that which was originally present in their 

 bodies. It is a well-known fact, moreover, that cattle which are fed 

 on nitrogenous food exclusively do not fatten, or only slightly so ; 

 whereas they soon gain in weight when a certain proportion of 

 carbohydrates is added to their food. 



The proportion of fat which is normally derived from albumins 

 is not very large, if we except the period of lactation in female 

 animals, but its possible origin from this source is undoubted. 



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