METHODS FOR STUDY OF DIGESTIBILITY OF LIPIDS 199 



In the first place, in order to insure greater accuracy, the experiments 

 were continued over a longer interval. The test period was nine days in- 

 stead of the three-day interval used in the earlier experiments. More- 

 over, the experimental period followed a two-day orientation during which 

 the diet was the same as that used throughout the nine-day period. 



In the second place, no markers were used. Since the subjects were 

 trained to have a bowel movement each morning, all stool samples were 

 collected except that evacuated on the morning on which the test began. 

 The collection included the sample excreted on the morning of the tenth 

 day following the start of the experimental period. Because of the rela- 

 tively long test period, any inaccuracy entailed in the separation of the 

 feces is considered to be minimal. 



Another variation in the procedure employed by Deuel, Johnson et al. A 

 involves the use of a much more varied diet, which was designed to over- 

 come the monotony. Actually, three different menus were employed, 

 which were rotated. The composition of typical menus is given in Table 1. 



Although the diets contained some extraneous fat other than the test 

 fat, about 88% of the total eaten represented the fat under investigation. 

 The amount of fecal fat originating from this extraneous fat was disregarded 

 in the calculations. 



Another modification in the present method involves the estimation 

 not only of neutral fat and fatty acids but also of that portion of the fat 

 excreted as soaps. Although this results in a considerably larger figure for 

 the total fecal fats, it apparently does not appreciably alter the figure for 

 digestibility, since the correction figure for metabolic lipids is likewise in- 

 creased when one includes the value for metabolic soaps. Deuel, John- 

 son et aZ. 4 estimate this value as 19.8% of the total dry weight of the stools, 

 as compared with the figure of 9.89% employed by Langworthy and 

 Holmes. 2 



(3) Methods for the Study of Digestibility of Lipids in Rats 



a. General Procedures. The procedures used for the tests with rats 

 are quite similar to those employed in the studies on human subjects. The 

 lipid under test is fed as a component of a standard diet. As in the case of 

 the second procedure described for man, a two-day orientation period is 

 used. During these two days the diet containing the fat under study is 

 fed, but the feces are not collected. Beginning on the morning of the third 

 day, a record is kept of the weight of the food given the rat, and all feces 

 on the pan of the cage are discarded. Typical diets employed in the rat 

 tests are listed in Table 2. 



