436 THE GLANDULAR ORGANS. 



Origin of the Albumins. Caseinogen, as has been stated, is a specific 

 product of the activity of the mammary glands, and 'is probably 

 formed from the complex nucleo-glucoproteid which occurs in the 

 functionally active organ. As this is not found in the milk, we may 

 conclude that after its formation it is decomposed and probably 

 yields casein, on the one hand ; while its reducing radicle may be 

 concerned in the production of lactose. 



Of the origin of lactoglobulin and lactalbumin, nothing is known ; 

 but, as I have said, the former is probably identical with the serum- 

 globulin of the blood, while in the case of the latter we may 

 imagine that it has originated through a peculiar transformation of 

 the serum-albumin. 



Isolation of the Albumins of the Milk. ISOLATION OF CASEIN- 

 OGEN. The milk is diluted with four times its volume of water and 

 acidified with acetic acid to the extent of 0.75-1.0 pro mille. On 

 standing, the caseinogen separates out and is filtered off. It is 

 purified by repeated solution in water with the aid of a little caustic 

 alkali, filtration, and reprecipitation with acetic acid. It is then 

 washed with water and freed from traces of fat by means of ether- 

 alcohol. The greater portion of fat remains on the first filter. 



ISOLATION OF LACTOGLOBULIN. The milk is saturated with 

 common salt in substance, which precipitates the caseinogen together 

 with a small portion of the globulin. If then the neutral filtrate is 

 . saturated with magnesium sulphate at 30 C., the remaining portion 

 of the lactoglobulin is obtained. This is purified as described in 

 the case of the serum globulin of the blood. 



ISOLATION OF LACTALBUMIN. The caseinogen and globulin are 

 first precipitated by salting with magnesium sulphate in substance at 

 30 C., and are filtered off. In the filtrate the lactalbumin can 

 then be demonstrated by acidifying with acetic acid to the extent 

 of a little less than 1 per cent, and boiling or by salting w r ith am- 

 monium sulphate or sodium sulphate in substance. The albumin 

 is filtered off and purified as described on page 339. 



Quantitative Estimation of the Total Albumins. To this end, a 

 few grammes of milk are diluted with water, treated with a small 

 amount of sodium chloride solution, and precipitated with tannic 

 acid or phosphotungstic acid in excess. In the precipitate, which is 

 washed with water, the amount of nitrogen is then estimated by 

 KjeldahFs method. By multiplying the result by 6.37 in the case 

 of cow's rnilk, or by 6.34 with human milk, the corresponding 

 amount of albumin is ascertained. The nitrogen of some of the 

 extractives is included in the result, but may be ignored. In cows 7 

 milk it represents about one-sixteenth of the total amount of nitro- 

 gen, and in human milk about one-eleventh. 



Separate Estimation of the Caseinogen and the Soluble Albumins. 

 A few grammes of milk are diluted with two or three volumes of a 

 saturated solution of magnesium sulphate, and are then saturated 

 with the salt in substance. In the precipitate, which is washed with 



