26 MANUAL OF HISTOLOGY 



( . C 18 H 83 



Triolein, C 3 H 5 \ . C 18 H 33 

 ( . C 18 H 33 



and also saponified with alkalies. 



It is introduced into the body with the neutral fats of the food. Its 

 physiological decompositions are probably manifold. 



REMARKS. It was formerly believed that margaric acid was the most widely-dis- 

 tributed of all animal fats. From the fact, however, that a mixture of equal parts of 

 palmitic and stearic acids has naturally the same composition as margaric acid, 

 C 17 H 32 2 , some have denied the existence of the latter altogether, but incorrectly, 

 for it has been produced artificially (Becker, Heintz). It is still a matter of doubt, 

 however, whether it and trimargarin are constituents of the ordinary fats of the body. 



18. 



In the foregoing section the constitution of the neutral fats which occur 

 naturally, have been brought before our notice ; we have also alluded to 

 the different fatty acids of these compounds. It is not possible to separate 

 one from the other, with any degree of accuracy, the individual neutral 

 fatty combinations which occur here, so that our acquaintance with the 

 latter is very unsatisfactory. They receive their peculiarities from the 

 fatty acids of the combination. 



Neutral fats, when pure, are colourless, without odour, and tasteless. 

 Their reaction is neutral, they are lighter than water, and bad conductors 

 of electricity. They are insoluble in water, but soluble in warm alcohol 

 and in ether. They give rise to fatty stains upon paper, burn with bril- 

 liant flame, and cannot be volatilised without decomposition. 



By the action of steam, heated up to 220 C., the neutral fats are split 

 up into acids and glycerin. The same effect is produced through the 

 agency of ferments, as, for instance, putrefying protein compounds. Ex- 

 posed to the air they greedily absorb oxygen, and with this and the com- 

 bined action of ferments, become rancid, water being absorbed and glycerin 

 and fatty acids set free. Further, by the action of alkalies in the presence 

 of water, they are decomposed and converted into soapy compounds, in 

 which process glycerin is set free, while the acid combines with the inor- 

 ganic base. 



It has been already remarked above, that the separation of the several 

 neutral fats from the natural fats of the human body is not possible. 

 Hence the questions in regard to their nature have been answered in various 

 ways. Berth clot, following up Pelouze, has recently composed the neutral 

 fats by artificial means out of glycerin and the fatty acids, and has thus 

 opened up a new way for the recognition of the fatty matters occurring 

 in the system. From the correspondence between their properties and 

 those of the natural fats, many of these compounded neutral fats have 

 been recognised as constituents of the body. 



They are, therefore, all of them, combinations, in which the three atoms 

 of H of the hydro xy Is of the glycerin are replaced by the corresponding 

 radicals of those fatty acids. Thus we have a compound corresponding 

 with elaidic acid, triolein, a fluid at ordinary temperatures, and then hold- 

 ing two other solid crystalline neutral fats in solution, namely, tripalmitin 

 and tristearin* It is still doubtful whether we have here all -the con- 

 stituents of the mixture of neutral fats occurring in the system. In butter 

 * To these may be added probably trimargarin. 



