306 PHYSIOLOGICAL CHEMISTRY. 



addition of lime-salts after cooling. The action of the rennet 

 enzyme on casein takes place also in the absence of lime-salts, and 

 these last are only necessary for the coagulation or the precipitation 

 of the paracasein. 



Casein may be prepared in the following way : The milk is di- 

 luted with 4 vols. water and the mixture treated with acetic acid to 

 0.75 to 1 p. m. Casein thus obtained is purified by repeated solu- 

 tions in water with the aid of the smallest quantity of alkali pos- 

 sible, by filtrating and reprecipitating with acetic acid, and 

 thoroughly washing with water. Most of the milk-fat is retained 

 by the filter on the first filtration, and the casein contaminated with 

 traces of fat is purified by treating with alcohol and ether. 



Lactoglobulin was obtained by SEBELIEX from cow's milk by 

 saturating it with NaCl in substance (which precipitated the 

 casein), and saturating the filtrate with magnesium sulphate. As 

 far as it has been investigated it had the properties of serum-glob- 

 ulin, with which it is perhaps identical. 



Lactalbumin was first prepared in a pure state from milk by 

 SEBELIEN. Its composition is, according to SEBELIEN, C 52.19, 

 H 7.18, N 15.77, S 1.73, 23.13 per cent. Lactalbumin has the 

 properties of the albumins. It coagulates, according to the con- 

 centration and the amount of salt in solution, at -f 72 to 84 C. 

 It is similar to serum albumin, but differs from it in having a con- 

 siderably lower specific rotary power; a (D) = 37. 



The principle of the preparation of lactalbumin is the same as 

 for the preparation of serum-albumin from serum. The casein and 

 the globulin are removed by MgS0 4 in substance and the filtrate 

 treated as previously stated (page 61). 



The occurrence of other albuminous bodies, such as albumoses and peptones, 

 in milk has not been positively proved. These bodies are easily produced as 

 laboration products from the other albuminous bodies of the milk. Such a 

 laboration product is MILLON'S and COMAILLE'S lactoprotein, which is a mix- 

 ture of a little casein with changed albumin, and which is formed by the 

 chemical operations. 



Milk-sugar, LACTOSE, C tt Hyf> u + H 2 0. This sugar with the 

 absorption of water can be split into two glucoses, dextrose and 

 galactose. It yields by the action of dilute nitric acid, besides 

 carbon dioxide, oxalic acid, tartaric acid, saccharic acid, and racemic 

 acid, a crystallizable mucic acid, which is nearly insoluble in cold 

 water and in alcohol, and which may also be obtained from dulcite, 



