Effect of Fibrin. 105 



coefficient of expansion of butter fat is more than three times as 

 great as that of water, so that in order to maintain the same 

 relative difference in their specific gravities, when the tempera- 

 ture is falling, the milk serum must cool more than three times 

 as rapidly as the fat. In other words, when the milk serum has 

 cooled from 90° F. to 40° F., or through 50°, the fat globules 

 should have lost less than 17°, and should still have a tempera- 

 ture of over 73° F., a difference between the temperature of the 

 fat and serum of more than 33°. Such a condition is mani- 

 festly impossible, but any less difference than this would cause 

 the fat to become relatively heavier than at first, and would 

 operate against the creaming. 



On the whole, the most satisfactory explanation of 

 the good effect of the low temperature in the deep 

 setting system is that advanced by Babcock,* that 

 the presence of fibrin in milk, especially when it has 

 coagulated in the form of threadlike masses, permeat- 

 ing the fluid in all directions, offers a considerable 

 obstacle to the rising of the fat globules. The sudden 

 reduction of the temperature quickly after the milk 

 is drawn, by preventing the formation of these 

 fibrin clots or threads, aids in the separation of the 

 fat. This would be entirely satisfactory were it not 

 for the fact that it has been shown that while it 

 is usually of advantage to cool the milk imme- 

 diately after it is drawn, in some cases, at least, 

 the setting and cooling may have been delayed for 

 a time long enough to permit the formation of 

 fibrin clots without appreciable effects upon the sep- 

 aration, as the following tables t very clearly show, 

 the efficiency of creaming being measured by the 

 percentage of fat in the skimmed milk: 



*Loc. cit. 



t Cornell University Agriciiltural Experiment Station, Bull. No. 29, p. 73. 



