34 Biological, Chemical and Physical Characteristics of Milk. 



gestion of milk at blood temperature for several hours was incorrect (Schmidt and Tier- 

 felder, likewise that casein is not produced by mixing blood serum and macerated milk 

 gland structure, or milk gland juice and ovalbumin, and especially since it is known that 

 casein represents a nuclear albumin containing phosphorus, the enzymic origin of the 

 casein in the above sense is denied. For a time Basch 's hypothesis relative to the origin 

 of the casein was accepted, namely that the nucleic acid which is set free in the alveoli 

 by the activity of the gland, combines with the transuded blood serum, forming the 

 nucleo-albumin, the "casein." Investigation of the experiments of Basch by Odenius, 

 Mendel, Levene and Lobisch proved however that Basch 's hypothesis cannot stand. 



At the present time it must be admitted that the cells of the 

 milk gland break up the proteids into more simple bodies, and then 

 build up the casein from these products. 



The casein is distinguished from other proteids containing phosphorus, as for in- 

 stance from the nucleo-proteids, by the absence of the xanthin group, the pyrimid.ins, 

 and the pentose group. The consistence of casein from various species of animals varies 

 chemically to a considerable extent. By special reactions with casein anti-serum 

 (precipitation, complement fixation), the caseins from different species of animals may 

 be differentiated one from the other. In the splitting up of casein into its various con- 

 stituents, quantitative differences in these split products are found which indicate the 

 differences in the individual caseins. 



The cow casein contains 

 according to C. H. S. P. N. 0. 



Tangl 52.99 6.81 0.832 0.877 15.65 23.141% 



Ellenberger .... 53.07 7.13 0.76 0.80 15.64 22.60 % 



Burow 52.825 7.095 0.725 0.808 15.64 22.906f 



Hammarsten ... 52.96 7.05 ^ 0.758 0.847 15.65 



It is insoluble in water and in alcohol, but with bases forms 

 solutions, the so-called casemates. Alkali-caseinates form opales- 

 cent solutions, while solutions from casemates of earthy alkalies 

 represent cloudy, milky fluids. Casein is slightly acid, the solution 

 of which with the bases is accompanied by the formation of salt-like 

 compounds. 



The characteristics of casein are of especial interest, as they 

 give to the milk its well known properties of rennet-coagulation, 

 and easy acid coagulation, etc. 



Casein is present in the milk as caseinate of lime, in suspended 

 condition as dicalcium-caseinate, which gives an acid reaction to 

 phenolphthalein, and a neutral reaction to litmus. 



Acid abstracts calcium from the caseinate, the casein being 

 precipitated (that is casein from the milk of cows and other rum- 

 inants) as coarse, flaky material, while the casein from the milk of 

 solipeds and women is precipitated as a fine, flaky substance. 



This difference in its properties is traceable to the physical condition which is mani- 

 fested by the casein molecule of the various kinds of milk (Fuld and Wohlgemut) ; but 

 it 7iiay also be the result of a variation in the quantity of salt and proteid present in the 

 milk. 



In the presence of di- and tri-phosphates the casein dissolves 

 by combining with a part of the bases, so that the neutral and alka- 

 line phosphates change into monophosphates (Hammarsten, 

 Arthus). 



