of Fat in the Alimentary Canal. 



251 



absolute composition of the fats present in the milk at the time of 

 administration was accurately known, and could be compared with 

 that in the various parts of the alimentary canal. 



2. The Chemical Analysis. — The substances collected from each 

 separate part were dried at 90° C, and then placed in a Soxhlet's 

 apparatus and extracted with ether until the ether was unable to 

 extract any more soluble matter. The ether extract was then dried 

 and re-dissolved in absolute ether of sp. gr. 0*720, and filtered 

 through a fat-free filter paper into a weighed vessel, in which it was 

 dried and afterwards weighed. 



The ether residue thus obtained was then treated with a watery 

 solution of sodium carbonate, which converted the free fat acids into 

 soaps, and after again drying, the neutral fat, cholesterin, &c, was 

 again extracted with ether and weighed. The difference between 

 this and the first weighing was taken as equal to the quantity of free 

 fat acids present. 



In some few cases quantitative estimation of the cholesterin was 

 made by saponifying the neutral fat extract with alcoholic sodium 

 hydrate, evaporating to dryness, and then extracting with ether. 

 This being repeated until saponification with alcoholic sodium hydrate 

 no longer removed any neutral fat, and it was found that the ether 

 extract consisted of cholesterin alone. 



The original substance which had been extracted with ether was 

 treated with dilute hydrochloric acid so as to liberate any fat acids 

 from the soaps that might be there present. It was then dried at 

 90° C, and when completely dry was again extracted with ether. 

 The quantity of ether extract thus obtained represented the fat acids 

 present in the form of soaps. 



The total fat was, therefore, obtained by adding the quantity of fat 

 acids obtained from the soaps to the former ether extract. 



To facilitate the comparison of the results in the experiments they 

 are given in tabular form, and the analysis of the diet in each part of 

 the alimentary canal is divided into groups, i.e., neutral fat, fat acids, 

 and fat acids combined as soaps. 



The neutral fat includes the cholesterin, which was not in the 

 majority of cases separately analysed, as the quantitative analysis of 

 -cholesterin is very much more difficult in practice than it is in theory, 

 since the entire saponification of the neutral fats, so as to separate 

 them thoroughly from cholesterin, is a tedious matter and requires 

 frequent repetition if one desires to get really accurate results. In 

 those few cases in which the analysis of cholesterin was carried out, 

 the quantity found was so extremely small that it in no way inter- 

 fered with the general results obtained if the entire extract was 

 regarded as neutral fat. 



