CHEMICAL BASIS OF THE ANIMAL BODY. 19 



Lieberkiihn 1 . Purified white of egg (see p. 11) is made into a jelly 

 by the addition with rapid stirring of strong caustic soda, avoiding as 

 far as possible all excess of the latter. The jelly is then cut into small 

 lumps and washed in distilled water, frequently changed, until the lumps 

 are quite white throughout. The lumps of purified albumin are then 

 dissolved in water by gently heating on a water-bath, the solution 

 filtered and the alkali-albumin precipitated by careful addition of 

 acetic acid. The precipitate is then thoroughly washed with distilled 

 water. The product thus obtained is very pure but there is a con- 

 siderable loss of material during the washing of the gelatinous lumps, 

 owing to the solubility of the substance in the alkali which is being 

 removed. The pure substance itself is also slightly soluble in water. 



4. Casein 2 . 



This is the well-known proteid existing characteristically in milk 

 and in no other fluid or secretion of the body 3 . 



It has recently been proposed to call this proteid ' caseinogen ' and to use the 

 name casein for the product of its decomposition, the clot or curd, which is formed 

 by the action of rennin upon it. This nomenclature would have the advantage of 

 indicating a relationship between the two proteids similar to that between fibrin 

 and fibrinogen, myosin and myosinogen (Halliburton). 



Preparation*. Fresh milk is diluted with 4 volumes of distilled 

 water and acidulated with acetic acid until the diluted milk contains 

 from -075 to Ol p.c. of the acid. If the milk has been diluted with 

 ordinary tap-water rather more acid must be added. The precipitated 

 casein is now washed two or three times by decantation with water, as 

 rapidly as possible, dissolved in the least quantity of dilute caustic soda 

 which suffices for its solution, and filtered through a series of filters 

 until the filtrate is quite clear and only faintly opalescent. This filtrate 

 is then somewhat diluted, the casein again precipitated by the careful 

 addition of acetic acid, and the whole process of washing, solution and 

 reprecipitation carried out a second time. The final product is now 

 freed as far as possible from water, worked up into an emulsion with 

 97 p.c. alcohol, collected on a filter, washed with alcohol, finally with 

 ether, dried by exposure to the air, and finally in vacuo over sulphuric 

 acid. 



1 Poggendorf 's Annal. Bd. LXXXVI. S. 118. 



2 Our knowledge of the chemistry and properties of casein are based chiefly upon 

 the researches of Hammarsten. His papers were mostly published originally in 

 Swedish or Latin, but are fully abstracted by himself in Maly's Jahresbericht d. 

 Thierchem., to which reference will in each case be made. 



3 For methods of conducting a complete analysis of milk see Pfeiffer, Die Analyse 

 der Milch, Wiesbaden, 1887. 



4 Hammarsten, Maly's Benefit. Bd. vn. (1877), S. 159. 



