163 



serum, so prepared tliat fibrin Avoiild form in it. was added to such an 

 emulsion the o-lobulos <2:rouped exactly as in milk. For chemical tests 

 peroxide of hy(h'o<>eii and <2,iiiacum were used and the reactions of 

 milk and blood fibrin were very similar. 



The effects of temperature upon the specific gravities of fat and 

 milk serum and upon the viscosity of milk are discussed. and experi- 

 ments described. The viscosity is found to decrease as the tempera- 

 ture rises. High temperature would, therefore, be favorable to cream- 

 ing if it were not for the formation of fibrin, which is aided by the 

 high, and hindered by low, temperature. With the centrifugal sepa- 

 rator the effect of the centrifugal force is to increase " the effective 

 difference in weight "" betw^een the lighter fat globules and the heavier 

 fibrin. The fat globules moA'c quickly to the center and escape 

 entanglement l)v the fibrin, while the latter gathers to a greater or less 

 extent on the drum of the centrifugal ; hence, high temperature favors 

 creaming with the centrifugal. The formation of fibrin helps to 

 exj^lain the delay in setting of milk. When milk stands for some 

 time before cooling, fil)rin forms, and the fat globules are entangled 

 in the clots and rise slowly. Warming the milk again after it is cool 

 does not mend the matter, because it does not integrate the fibrin 

 (lots. But if milk is cooled on ice as soon as drav/n from the cow the 

 fibrin does not form so (juirkly and creaming is more complete. 



Coagulation of fibrin may be prevented by various chemicals, as is 

 clearly illustrated by figures from micro- photographs and by numer- 

 ous exi^eriments in which the cream rose rapidly from milk to which 

 about one-tenth of 1 per cent of caustic soda was added. The fat left 

 in the skim -milk was less and the butter product was greater when the 

 caustic soda was added. The practical objections to the use of chem- 

 icals are that special training is required and that the value of the 

 skim-milk is impaired. 



The following conclusions are drawn by the author from his experi- 

 ments and collateral considerations: 



(3) That niilk when fresh is :i perfect enmlsion, the fat globules being free 

 and without an envelope. 



(2) That the chief differences in the composition of normal milks are due to 

 variations in the amount of fat, the remainder of the milk, known as the milk 

 serum, being quite uniform in composition in all milks. The variation in the 

 amount of serum solids in milk from the same cow is rarely more than one-half 

 Iier cent, in milk from different cows of the same breed it is usually less than 1 

 per cent, and in milk from cows of different breeds not more than 2i per cent. 

 'J'his holds true even when the fat varies as nuich as 7 or 8 per cent. 



(o) That milk contains a principle <Mnalog(ms to or identical with blood fibrin 

 which is capable of spontaneous coagulation, the clots of which entangle the fat 

 globules and to a considendde extent prevent an efficient creaming. 



(4) That the most etiicient creaming is obtaintnl when conditions ai-e supplied 

 which retard or prevent the coagulation of fibrin. This may, in practice, be best 

 acconiplished by setting the milk directly after milking in cold water, the cream- 

 ing vessel to be of bright tin or other jnetal that can easily be kept clean. 



(.5) When the milk is transported, or when for any reason the setting must be 

 delayed, no method of creaming gives as satisfactory results as the centrifugal. 



