206 III. DIGESTIBILITY OF FATS 



the experiment until the samples of feces may be collected for the test. 

 Moreover, it was noted that the results were reliable only when the ratio 

 included ground feed with which the Cr 2 3 could be premixed; when the 

 chromic oxide was added to an unground all-roughage ration, it was 

 partially retained, leading to unreliable and low estimates of digestibility. 

 It was found that, when these precautions were observed, the results 

 were satisfactory provided they were based upon analyses of a composite 

 sample prepared from random samples taken over four days. The chromic 

 acid method has been employed successfully in the case of horses, 22 - 30 

 pigs, 28 and calves. 28 Kreula, 31 ' 32 Virtanen, 33 and Irwin and Crampton 34 

 found that the chromic acid procedure gives satisfactory results with 

 human subjects. Kreula 31 was able to recover as much as 97.2% of the 

 chromium oxide fed. Finally, Schurch, Lloyd, and Crampton 35 carefully 

 evaluated the use of chromic oxide as an indicator substance in the rat. 

 It was found that identical results for digestibility were obtained when 

 analyses of random samples obtained at various periods of the day were 

 used for the calculation. 



The recovery of chromic oxide has been proved to be quantitative in 

 cows. Thus, Kane, Jacobson, and Moore 19 observed the following re- 

 coveries of ingested Cr 2 3 in cows: Cow 65, 100.0% (101.8-97.8) ; Cow 54, 

 100.4% (102.1-97.3); and Cow 10, 99.3% (101.0-96.7). This gave a 

 grand average recovery of 99.9% for all tests with cows. 



e. Indigestible Chromogenic Substances as Inert Materials in the De- 

 termination of Digestibility. Reid et oL 36 ' 37 used indigestible chromogenic 

 materials as indicators for digestibility in ruminants. The feed and feces 

 were extracted with 85% acetone, and the concentration of chromogenic 

 material in the resulting colored extract was determined by means of a 

 spectrophotometer at 406 m/*. Anthraquinone violet is one chro- 



30 N. Olsson, G. Kihlen, and W. Cagell, Lantbrukshogskol. Husjiirsforsokanstalt., 

 Medd., 36 (1949); cited by A. F. Schurch, L. E. Llovd, and E. W. Crampton, /. Nutri- 

 tion, 41, 629-636 (1950), p. 630. 



31 M. S. Kreula, Biochem. J., 41, 269-273 (1947). 



32 M. S. Kreula, "Die Resorption des pflanzlichen Carotins aus dem Darmkanal des 

 Menschen," Univ. Helsinki, Agr.-Forshoissensch. Fakultdt (1950); cited by M. I. Irwin 

 and E. W. Crampton, J. Nutrition, 43, 77-85 (1951). 



33 A. I. Virtanen, Personal communication; cited by A. F. Schurch, L. E. Lloyd, and 

 E. W. Crampton, /. Nutrition, 41, 629-636 (1950), p. 630. 



34 M. I. Irwin and E. W. Crampton, J. Nutrition, 43, 77-85 (1951). 



35 A. F. Schurch, L. E. Lloyd, and E. W. Crampton, J. Nutrition, 41, 629-636 (1950). 



36 J. T. Reid, P. G. Woolfolk, C. R. Richards, R. W. Kaufmann, J. K. Loosli, K. L. 

 Turk, J. I. Miller, and R. E. Blaser, /. Dairy Sri., 33, 60-71 (1950). 



37 J. T. Reid, P. G. Woolfolk, W. A. Hardison, C. M. Martin, A. L. Brundage, and 

 R. W. Kaufmann, /. Nutrition, 46, 255-269 (1952). 



