204 III. DIGESTIBILITY OF FATS 



with some feeds which, because of their physical nature, were unsuitable 

 for the use of this marker. 



b. Lignin as an Inert Material in the Determination of Digestibility. 

 There have been quite diverse reports as to the applicability of lignin as 

 an indicator substance in digestibility tests. Hale et al. 12 reported that 

 the use of lignin ratios was an unsatisfactory method for determining 

 digestibility. The results of Forbes and associates 14 on cattle might like- 

 wise be interpreted as proving the non-applicability of lignin. These 

 latter investigators were able to demonstrate instances in which the co- 

 efficient of digestibility was 29, although their results showed wide varia- 

 tions which, in some cases, gave negative values. Crampton and Jackson 1& 

 likewise found that the use of lignin yielded unreliable results. 



On the other hand, a number of workers have reported excellent results 

 with this polysaccharide. Ellis, Matrone, and Maynard 16 found that 

 lignin was not digested to any significant degree, while Swift and col- 

 laborators 17 considered that, in ruminants, the use of lignin produced 

 highly valid results. Moreover, Forbes and Garrigus 18 applied the lignin 

 technic successfully for the determination of the nutritive intake of grazing 

 animals. A later report of Kane, Jacobson, and Moore 19 has shown that 

 lignin is not absorbed, and that its use "shows promise of saving much of 

 the time, labor, and expense involved in the present cumbersome method 

 of conducting digestion trials." The recovery of ingested lignin in the 

 feces of cows was as follows (6 experiments in each case) : cow 65, 100.3% 

 (103.4-97.4); cow 54, 99.0% (103.4-96.4); cow 10, 97.2% (100.3-95.4). 

 This gave a grand average of 98.8% for recovery, which is certainly within 

 the range of experimental error. The comparison of results obtained by 

 the use of lignin and of chromic oxide is illustrated in Table 5 (p. 207). 



c. Silica as an Inert Material in the Determination of Digestibility. 

 Silica (silicon dioxide, SiOo) is another material which has been proposed 

 as the inert substance for the calculation of digestibility. However, it 

 has been claimed that dust in barns or dirt on food may be sufficient to 

 invalidate the results when silica is used as the indicator. Moreover, 



14 E. B. Forbes, R. W. Swift, J. W. Bratzler, A. Black, E. J. Thacker, C. E. French, 

 L. F. Marcy, R. F. Elliott, and H. P. Moore, Perm. Slate College, School Agr., Agr. Expt. 

 Sta., Bull. No. 452, 1-34 (1943). 



16 E. W. Crampton and I. R. C. Jackson, J. Animal Set., S, 333-339 (1944). 



16 G. H. Ellis, G. Matrone, and L. A. Maynard, J. Animal Sci., 5, 285-297 (1946). 



17 R. W. Swift, E. J. Thacker, A. Black, J. W. Bratzler, and W. H. James, J. Animal 

 Sci., 6, 432-444 (1947). 



18 R. M. Forbes and W. P. Garrigus, J. Animal Sci., 7, 373-382 (194S). 



19 E. A. Kane, W. C. Jacobson, and L. A. Moore, J. Nutrition, 41, 583-596 (1950). 



