17,2 Adriano: Determination of Lactose 219 
soluble products not precipitated by acid mercuric nitrate. The 
proteins or milk are most susceptible to hydrolysis during the 
process of evaporation, and would give rise to optically active 
products which may not be precipitated by mercuric nitrate. 
To test this point the filtrates from samples 7 to 10, 11 to 14, 
and 15 and 16 (Table 3) were analyzed for their nitrogen con- 
tent by the Kjeldahl Gunning Arnold(8) method with the fol- 
lowing results: 
TABLE 5.—Nitrogen determination of filtrates from samples 7 to 10, 11 to 
14, 15 and 16 (Table 3). 
Nitrogen in samples— 
Source of sample. 
7 to 10. | 11 to 14. |15 and 16, 
Per cent.|Per cent.|Per cent. 
Filtrate for the polariscopic method -------------------------------+ 0.0110 0.0180 | 0.0021 
Calculated as milligrams alanin in 100 cubic centimeters of filtrate.| 70.00 82. 50 12. 70 
Filtrate for the reduction methods--_-_...------ 0. 0006 0.0056 | 0.0016 
These results show that hydrolysis of the protein occurs in 
the process of evaporation and sterilization of milk. Thus the 
fresh cows’ milk gives less nitrogen in the filtrate than either 
the evaporated or the sterilized milk. The differences are 
clearly seen if the nitrogen is expressed in milligrams of a 
dipeptid or an amino acid such as alanin. Of course, nothing 
is known of the nature of these nitrogenous compounds. But, 
judging from the results of the analysis of samples 7 to 10, 
where the average difference between the polariscopic method 
and the two oxidation methods is greater than 1 per cent, and 
of samples 11 to 14, where the optical and the oxidation methods 
agree to within 0.1 per cent—both giving almost the same per- 
centage of nitrogen in the filtrate—these soluble products may 
influence the rotation of lactose in either direction. It is very 
likely that other factors have an influence on the specific rotation 
of this sugar. This seems to be indicated by the results with 
synthetic milk. The casein used in the preparation of the 
latter must have been completely reprecipitated together with the 
fat by the acid mercuric nitrate, since hydrolysis of the casein 
was hardly possible under the conditions of the experiments; 
and yet the results of the sugar analysis by the polariscopic 
method are much lower than by the oxidation methods. Of 
course, no definite conclusions can yet be drawn from the results 
of only one set of experiments, but there are some indications 
