270 HALOIDS AND HALOID BASES. 



If we assume that the fats are subjected to so gradual an oxidation 

 that their carbo-hydrogen radical gradually diminishes by 2 atoms 

 of carbo-hydrogen, it is singular that we should find the fatty 

 acids which mark the gradations from capric to margaric acid in 

 plants, but not in animals ; for while the formation of fatty acids 

 with a high atomic weight is very gradual in plants, a similar law 

 does not prevail in reference to their regressive formation in 

 animals, for here we meet with no acids besides margaric and 

 stearic having a fat-radical of the formula, C n H n _ 1 . It would 

 appear, therefore, that the fatty acids, when separated from glyce- 

 rine (to which reference has already been made at p. 243) enter 

 into complicated combinations and metamorphoses, in which it is 

 not easy to recognise or detect their presence. We have already 

 (at p. 126) noticed the probability that the principal acid contained 

 in the bile, cholic acid, is a conjugated fatty acid ; chemical experi- 

 ments giving evidence of the presence of oleic acid in it, although 

 it cannot actually be separated. 



The hypothesis, that a portion of the fat takes part in the forma- 

 tion of bile, is further confirmed by numerous physiological and 

 pathological experiments. 



The following physiological facts in some degree confirm this 

 view. A close observation of the development of the chick 

 within the egg, leads us almost irresistibly to the opinion, that 

 towards the close of the period of incubation, a portion of the fat 

 in the yolk-sac (when it is drawn into the abdominal cavity 

 and adheres to the liver) is converted into biliary matter ; and 

 every physiological enquirer, who has occupied himself with this 

 subject, must have observed the greenish tint which is often, 

 although not always, very distinctly visible in the yolk-sac, and 

 especially along the course of the veins. On one occasion I found 

 this colour so intense, that I was induced to treat the whole of the 

 yolk-sac and its contents with boiling alcohol, and examine it for bile, 

 according to the method described at p. 123 ; when the ordinary 

 bile-reaction was obtained by Pettenkofer's test. The veins of the 

 yolk-sac pass into the liver, and it is well known that the vessels of 

 the yolk-sac for the most part resorb the yolk, and transfer it into the 

 liver; for the earlier view that the yolk passes through the ductus 

 vitello-intestinalis\r\to the intestine, and is carried from thence into 

 the liver by the biliary ducts, is incorrect. The liver at this period 

 serves mainly, as E. H. Weber,* and Kollikerf have shown, to 



* Zeitschr. f. rat. Med. Bd. 4, S. 160-164. 

 t Ibid. Bd. 4,8. J 12-160. 



