MILK-FAT. 19 



milk on the one hand, and the mineral salts on the other. All influences 

 that are able to change the constitution of the salts of milk, such as the 

 prolonged action of high temperature, the evolution of carbonic acid from 

 milk fresh from the cow, the formation of lactic acid through fermentation, 

 the diseases of cows, their feeding, the time since calving, the age of the 

 cow, the boiling of milk, &c., also exercise an influence on the nature and 

 properties of the nitrogenous substances, especially on the caseous matter. 

 They alter to a slight extent the specific gravity of the milk, cause the 

 rising of the cream to take place either more rapidly or more slowly, and 

 make the milk more susceptible, less susceptible, or entirely unsusceptible, 

 to the action of rennet. They favour or retard its coagulation by acids, 

 and influence the nature of the curd produced by the action of rennet or 

 acids. 



6. Milk-fat (Butter-fat). Milk-fat is present in milk in a very 

 fine state of division, viz., in the form of innumerable little drops or 

 globules of varying size, which are all oo 



of them invisible to the naked eye. 

 In the milk of cows the diameter of 

 the smallest and the largest of these 

 globules is respectively '0016 mm. and 

 01 mm., so that the former is almost 

 6-25 times as small as the latter (fig. 17). 

 The globules vary in size between 

 these limits, and are present in vary- 

 ing proportions. It appears probable ^^ axtMon; &> large nes f und 

 that the number of the different-sized 



globules is in inverse ratio to their size, or, what is the same thing, 

 the weight of the sum of all the globules of the same size is 

 equal for the entire number of different sizes. At anyrate, the 

 microscopical examination of milk shows that the smaller the 

 globules the more numerous they are. 



Under the ordinary conditions which prevail in Germany, the 

 percentage of fat in cows' milk, with very few exceptions, varies 

 between 2'5 and 4'5, and may be stated, on an average, at 3*4. For 

 the north and north-east of Germany, the average may be stated at 

 3-25. 1 



1 The average of all complete American analyses of milk made up, 1891, is 4% of fat, the 

 limits being from 2 to 8%; while the average of over one hundred and twenty thousand 

 samples of English milk, as analysed by Dr. Vieth, is 4*1% of fat. (See Aikman's Milk: its 

 Nature and Composition (A. & C. Black), p. 11.) English Editors. 



