New York AGRICULTURAL EXPERIMENT STATION. 25T 
into fine threads when warm. This substance we regard as 
resulting from the combination of acid with the base-free casein, 
forming a casein salt of the acid used. Our reasons for believing 
that there is actual chemical combination between the casein and 
acid are the following: 
(ist) When a given amount of base-free casein is treated with 
an acid, a quite definite and constant amount of acid appears 
to be neutralized. In the case of +. hydrochloric acid, one gram 
of base-free casein appears to combine with about .5 cc. of acm. 
~(2d) The phenomenon of combination between proteids and 
acids appear to be very general, as shown by Cohnheim and 
others.?° 
(3d) When base-free casein is treated with an acid, it under- 
goes a marked change in its properties. 
(4th) While the combination is comparatively weak, it appears 
to be as strong as in the case of some quite stable inorganic 
salts. The fact that the acid can be completely removed by 
long-continued trituration with water does not constitute an 
argument against combination, since some well-known inorganic 
salts behave the same way under similar treatment. 
(5th) By treating base-free casein with a given amount of 
acid, we form the compound insoluble in warm dilute salt solu- 
tion and hot alcohol. By removing the acid from this latter 
compound, we obtain again the base-free casein with a restora- 
tion of its recognized properties of solubility and_ plasticity. 
Kiach of these compounds can be converted into the other by 
addition or removal of acid. 
THE RELATION OF CASEIN AND ITS COMPOUNDS TO 
PARACASEIN AND ITS COMPOUNDS. 
The coagulum formed by the calcium casein of cows’ milk when 
treated with rennet enzym was called by Hammarsten'™ ‘“ Kase.” 
Schulze and Rose’? suggested the name “ paracasein” for this 
product and their suggestion has been very generally accepted. 
There is still, however, much confusion as to the exact. applica- 
tion of this term, as we shall point out later. 
10 Chemie der Eiweisskérper, pp. 106, 114, 2d Ed. 1904. 
™ Maly Jahresber, d. Thierchem., 4:138 (1874). 
@ Tanduirth. Versuchs-Sta., 31:131 (1884-5). 
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