252 USES OF FAT. 



the production of heat by immediate and final oxidation into carbonic 

 acid and water. 



It is not to be supposed, however, that this final oxidation into car- 

 Fats undergo bonic acid and water always takes place at once or abrupt- 

 ^nslVthe a " ly* Every thing shows that fats pass through successive 

 system. gradations of retrograde metamorphosis, perhaps gradually 



losing by oxidation two atoms of carbon and hydrogen ; and, indeed, 

 there is reason to believe that, on special occasions, the opposite changes 

 happen. Thus stearic acid may arise from margaric acid by deoxidation. 

 It does not occur to any considerable extent in vegetable food, having 

 thus far been only found in cacao butter. 



In a summary of the uses of fatty substances may be mentioned the 

 Summary of production of a high temperature by oxidation ; their agency 

 the uses of fat. j n metamorphosis, as displayed by the assistance they lend 

 in gastric digestion; the function they seem to discharge in cell life, 

 which would appear to be important if it be true that the nuclei of some 

 cells are composed of fat ; their relation in the formation of bile, and their 

 probable connection with the production of haematin. Among, their phys- 

 ical uses may be mentioned the equable manner in which they propagate 

 pressures in all directions when they are in the liquid state, as is often 

 the case ; the manner in which they fill up vacuities, and communicate a 

 roundness and solidity to the system ; their low conducting power as 

 respects heat, which enables them to economize the warmth of the body ; 

 their diminishing of friction among moving parts, as in the case of the 

 muscles ; and that they discharge some highly important function as 

 respects the nervous system is proved by the manner in which they 

 uniformly occur in tubular nervous tissue. In the general metamorph- 

 oses of the system they seem to take an important part. This may 

 be inferred from the fact of their presence wherever cells or fibres are 

 forming. 



From what has been said respecting the connection of the fats with 

 the metamorphoses of the system, it is obviously incorrect to regard them 

 as constituting a purely respiratory element. 



Conclusions similar to those which have been stated respecting the 

 Nutrition of ve g eta ^ e source of the fats might also be arrived at as re- 

 the nitrogen- gards the source of the nitrogenized constituents of the sys- 

 tem. These likewise are found in plants ; and thus, therefore, 

 though the carnivorous animal may be said to be nourished by the car- 

 cass on which it feeds, it is nevertheless strictly true that its nutrient 

 material is all from the vegetable world. 



The repair of muscles, of nerves, of the skin, or other such highly or- 

 ganized parts, is dependent on the agency of cells. Since these are un- 

 distinguishable, or to all appearance perfectly alike, it becomes a matter 



