32 SCIENCE AND PRACTICE OF DAIRYING. 



milk, except water. These amount, on an average, for Germany, in 

 the case of the day's milk of large herds, to 12*25 per cent. 1 The per- 

 centage of fat may be stated at 27'75 of the total solids, and 3*4 per 

 cent of the whole milk, and the specific gravity at 15 C., at 1-334. 

 By deducting the percentage of fat from the total solids, the non-fatty 

 solids are obtained. These amount to 8'85 per cent of the whole milk, 

 and have a specific gravity, which remains very constant, of T6. 



The annual returns show that the specific gravity, for comparatively 

 large herds, if expressed in the form of degrees, 2 rarely rises or falls 

 more than 10 per cent, for milk of the different milking-times, taken for a 

 whole year. Similarly, the rise or fall of the percentage of fat rarely exceeds 

 30 per cent, of total solids 14 per cent, and of "solids not fat" 10 per cent. 



The percentage of the several constituents in milk, obtained at different 

 milking-times, from comparatively large herds, in the course of a year, 

 seldom falls below 2*4 per cent of fat, 10*5 per cent of total solids, 7 '8 of 

 "solids not fat", and 1*028 specific gravity. The specific gravity of the 

 total solids rarely exceeds 1*37. 



In the case of the milk of single milkings of single cows the limits 

 above stated are, of course, largely exceeded. It is almost unnecessary to 

 cite examples for the purpose of showing to what extent this may take 

 place in certain cases. The milk of single cows, for example, as has been 

 observed by the author, may contain, when the cow is in heat, less than 

 1 per cent of fat, and shortly before becoming dry as much as 8 per cent. 

 The greatest variation among all the constituents is found in the milk-fat, 

 and the least in the " solids not fat ", and the specific gravity. For this 

 reason, in testing milk, for the purpose of forming an opinion of its 

 quality, the determination of the specific gravity and of the "solids not 

 fat " are of especial value. 



Few observations have been made with regard to the variation in the 

 percentage of the nitrogenous matter and the milk-sugar. 



11. The Relation between the Specific Gravity of Milk and its 

 Percentage of Fat and Total Solids. That there is a relation between 

 the specific gravity of milk and its percentage of fat and solids is 

 clear; and it is obvious that these three factors are dependent on 

 one another. It is open to question whether the ratio between these 



*The average percentage of total solids in English milk, according to Vieth, may be 

 taken at 12'90 per cent, and that of the fat at 4'1 per cent; while the total solids in American 

 milk may be taken at 13 per cent, and that of the fat at 4 per cent (Aikman's Milk: Its 

 Nature and Composition, Chapter II. A. & C. Black). 



* The thousandth part of the specific weight is called a degree. The specific weight 

 1-0332 expressed in degrees would therefore be 33 '2. 



