i io THE CHEMICAL CONSTITUTION OF THE PROTEINS 



out the estimations in the resulting solution, whilst Nollau filtered the 

 hydrolysed solution. In practically all cases the humin nitrogen value 

 was found to be very high and is due to the effect of the presence of 

 carbohydrate (see p. 65). In spite of the errors introduced in the 

 analyses by the presence of carbohydrate, the authors consider that the 

 data are of extreme value for judging the food-value of the food-stuffs, 

 in respect of the constituent amino acids. The data are given on page 

 1 34. Marked differences are noticeable in the various food-stuffs. 



The influence of the presence of carbohydrate upon the results of 

 the analysis by the Van Slyke method has been investigated in the 

 case of caseinogen by Hart and Sure [1916] and of fibrin by Gortner 

 [1916]. Osborne, Van Slyke, Leavenworth and Vinograd [1915] 

 hydrolysed lactalbumin under the same conditions. 



Hart and Sure found that variations of the different figures occur 

 to a great extent and that they differ with the nature of the carbo- 

 hydrate. The changes in the data are especially apparent in the 

 amount of di-amino acids or hexone bases. Loss of nitrogen occurs in 

 the mono-amino acids in the presence of starch and xylan. It is not 

 possible to correct the data. They concluded that the Van Slyke 

 method was not applicable to the determination of the distribution of 

 nitrogen in food-stuffs, not even for comparative figures that could be 

 of any value. Such great variations were not observed by Osborne, Van 

 Slyke, Leavenworth and Vinograd, nor by Gortner. These workers 

 used a limited amount of carbohydrate, which never amounted to the 

 large quantity present in the natural food-stuff in relation to the amount 

 of protein. In all cases the most noticeable change in the data was 

 in the humin nitrogen. Gortner agreed with Hart and Sure in the 

 general conclusions and pointed out that this method of analysis of 

 proteins was accurate only with pure proteins, a statement emphasised 

 originally by Van Slyke. Considerations of this nature must also be 

 applied to Drummond's data with tissues which contain other natural 

 substances as well as proteins. 



Conclusion. 



The analytical data show that our methods of determining the com- 

 position of proteins are far from satisfactory. Some of the methods 

 have been adapted too exclusively to the solution of one particular 

 part of the whole protein ; co-ordination of methods should bring about 

 a better knowledge. The introduction of any new method has always 

 advanced the study of the chemistry of proteins, and the final solution 

 will probably result from the employment of new methods. 



