ANNUAL REPORT, 1939 31 



the cooked, frozen, and canned samples had lower results with the water extrac- 

 tion, probably due to heat coagulation of the protein and in the canned samples 

 a loss from the liquor. 



The enzymatic digestion using HCl and pepsin showed no effect resulting 

 from the continued storage period. In fact, all pairs (cooked and raw) were in 

 very good agreement. 



In vitro digestion using Na2C0g 4-trypsin showed no real differences but 

 indicated that 76.5 percent of the protein was digested regardless of length of 

 storage or method of preservation. 



In both cases, the insoluble ash and the insoluble residue were higher in the 

 cooked than in the raw samples regardless of the time of storage. If solubility 

 means availability there is more of these in the raw samples than in the cooked. 



This work is now complete for a sample high in starch, one high in protein, 

 and one high in roughage. These results will be evaluated as a whole before fur- 

 ther work is attempted. 



Investigations of Some Physical and Chemical Properties of Mosaic Viruses. 



(M. E. Freeman.) The investigations on potato mosaic under this project can 

 be carried out only during the fall and winter months. Because of delays oc- 

 casioned by hurricane damage in the fall of 1938, no experiments were attempted 

 during the winter of 1938-1939. 



Lignin and its Relation to the Absorption of Minerals by Plants. (Emmett 

 Bennett.) The chemistry of lignin is being studied to determine its role in plant 

 metabolism, to ascertain possible relationships with other plant products, and to 

 understand the properties which make it possible for this substance to function 

 as it does in the soil. 



Lignin was isolated from corn cobs by an alkali method. The purified product 

 was elect rod ialyzed in a Mattson cell. A partial study was then made of the 

 solvate obtained by dispersing lignin in a solution of sodium hydroxide. Electro- 

 metric titration of the solvate with hydrochloric acid yielded data which produced 

 a symmetrical curve with two inflection points. The first point came at about 

 pH 9 and the second at about pH 5. Precipitation occurred and seemed com- 

 plete at pH 5 ±0.1. 



Lignin dispersed in a solution of equal parts of alcohol and acetone and titrated 

 in the same way behaved differently. The addition of lignin alone to this solution 

 lowered the pH to a point below which precipitation occurred in the previous 

 solution. Precipitation did not occur upon lowering the pH to 2.5. 



These data indicate that lignin prepared in the manner described may differ 

 from humates in the soil in at least two ways: (1) Neither charge nor hydration 

 appears to be the stability factor; (2) Solvation does not occur at a pH below the 

 precipitation zone. 



Lignin appears to be different from other incrusting materials such as hemi- 

 cellulose in that these substances usually have the two stability factors, charge 

 and hydration. 



Precursors of lignin. The work discussed in the last report has been written 

 up and two papers have been submitted for publication. 



The Digestibility of Lignin. Previous work with rats showed a high percentage 

 recovery of lignin and indicated a decrease in the digestibility of nitrogen. In 

 1939 the digestibility of lignin and the effect of a diet of high lignin content on 

 the digestibility of nitrogen was determined. 



Rats were fed a complete diet containing 15 percent of lignin which had been 

 isolated from corn cobs. An average of 93 ±3 percent of the lignin was recovered. 



