178 H. S. H. WARDLAW. 



ethereal layer was therefore 51-6 ce, and that of the aqueous 

 layer 19-0 cc. Twenty cc. of the ethereal layer were pipetted off 

 and the spirit was driven off in a weighed vessel. The fat which 

 remained behind weighed 0-1257 gm. The percentage of fat in 

 the milk was therefore: 0-1257/10 x 51-6/20 x 100/1-030 or 

 3*14, the density of the milk being taken as 1-030. Ten cc. of 

 the aqueous layer were now pipetted off and the protein in this 

 liquid was precipitated as described above The dried precipitate 

 weighed 0-1146 gm. The percentage of protein in the milk was 

 therefore; 0-1146/10 x 190/10-0 x 100/1 -030 or 2-1 I. 



The following series of estimations of the amount of 

 protein in human milk show the degree of concordance 

 which is attainable between individual estimations on the 

 same sample by this method: 



Sample A. 



Sample B. 



Sample O, 



2-62% 



3-20% 



2-59% 



2*63 



3*22 



2*57 



2*60 



3'21 



2*56 



2*63 







2-62 







The results obtained by this method thus agree together 

 to within about 1%. 



In order to ascertain whether the results obtained by 

 this method are strictly comparable with those obtained 

 by the method of Sikes, six estimations of the amount of 

 protein in a sample of milk were carried out by each method. 

 The mean result of the six estimations by Sikes' method 

 gave the percentage of protein as 1*36, while the mean of 

 the six estimations by the present method gave the per- 

 centage as 1*35. The two methods therefore give closely 

 agreeing results. The percentages of protein are given to 

 one part in one hundred in the accompanying tables. 



Of the remaining constituents of human milk, which 

 have not been directly estimated, 90% are made up of milk 

 sugar. The chief other substances present are: ash 0*2%; 

 nitrogenous extractives, principally urea, 0*2%; citric acid 



