162 



milk; illustrates the iliscussions by results of experiments at the Sta- 

 tion and elsewhere; and shows the bearing of the facts upon the 

 creaming of milk and the proper methods of handling milk and of 

 making of butter. 



Milk -fihrm. — The announcement that besides casein and albumen 

 there is in milk a nitrogenous compound similar to the fibrin of blood 

 was made by the author in 1888.* To this he gives the name fibrin, 

 milk fibrin, or lacto fibrin. The observations w^hich led to this impor- 

 tant conclusion and the chemical and other tests by w^hich it is sup- 

 ported are stated in some detail in the bulletin. 



The theory on which the author proceeds is, in brief, that the fibrin 

 of milk, like that of l)lood, is an albuminous substance which sepa- 

 I'ates by coagulation in the form of minute, elastic fibers. These make 

 a network in which the corpuscles of blood or the fat globules of milk 

 are entangled. In blood large clots are thus formed, while in milk, 

 in which the amount of fibrin is extremely small, the clots are too 

 minute to be seen with the naked eye. If milk is put under the 

 microscope as soon as drawn, there is no appearance of fibrin and the 

 globules are diffused uniformly through it; in other words, it has the 

 appearance of a ]>erfect enndsion of fat in milk serum. But fibril 

 forms soon and clots containing fat globules are speedily visible. 



Observations and experiments cited indicate that in milk as ordi- 

 narily handled *" the coagulation of fibrin begins at the surface and in 

 contact with the sides of the vessel ; that it is hastened by contact wuth 

 any rough surface, by agitation, and by exposure to air; and that it is 

 retarded by cold and by certain chemicals." Since the amount of 

 fibrin in normal milk is very small, the influence of its weight alone in 

 promoting the rise of fat w^ould not be very important. Indirectly, 

 however, these clots have a decided influence, " entangling not only 

 the fat, but the other matters, solid and gelatinous, in the milk, which 

 are either carried into the cream, or, if the solid portions are too 

 heavy, are prevented from rising at all." In short, the clots of milk 

 fibrin with the fat globules entangled in them are slower to rise than 

 are the fat" globules when alone and untrammeled by the fibrin. 

 Hence fibrin tends to hinder the creaming of milk. AVhatever tends 

 to favor the formation of fil)rin clots or to prevent their rising when 

 formed is, in so far, unfavorable to the rising of cream. Whatever 

 tends to preA^ent the formation of fibrin is h(dpful to creaming. 



Observations with the microscope, experiments wnth artificial emul- 

 sions, and chemical tests developed marked analogies between the 

 fibrin of milk and that of blood. In both milk and blood the forma- 

 tion of fibrin and the grouping of corpuscles begins after the milk or 

 blood is drawn, and can be prevented by sodium and potassium 

 hydrates or by various salts. Artificial emulsions with no material 

 to supply fibrin showed no tendency to grouping, but when blood 



* In a paper read at Cleveland, Ohio, August, 1888, before the Society for the 

 Promotion of Agricultural Science. 



