CHAP. v. VARIATIONS IN COMPOSITION OF MILK. 297 



of vinegar will cause a portion of what was left to coagulate. What 

 remains after both of these coagulated principles have been removed is 

 whey, containing sugar of milk, some nitrogenous substance, lactic 

 acid, and various salts. 



Some exact information upon the composition of milk is given by 

 Dr. Paul Vieth, Analyst to the Aylesbury Dairy Company, in an 

 elaborate paper published in the "Journal of the Royal Agricultural 

 Society of England," vol. xxv., 1889. He discusses the results of 

 anatyses of no less than 84,746 samples of milk, made during a period 

 extending over eight years. The samples analysed were the produce 

 of herds kept upon English dairy farms, and Dr. Vieth records the 

 results in a series of diagrams indicating the total solids, the non-fatty 

 solids, and the fat, according to the monthly averages of eight years. 

 It is premised that the total solids include everything that is valuable 

 in milk ; the fat must, in several respects, be considered the most 

 valuable component part ; and the percentage amount of non-fatty 

 solids is of particular importance as being the most constant factor, 

 and, therefore, best adapted to serve as a guide to the genuineness 

 and purity of the milk. It is hardly necessary to remind our readers 

 of the fact which may be tersely expressed, so far as milk is concerned, 

 thus : 



TOTAL SOLIDS = NON-FATTY SOLIDS + FAT. 



Dr. Vieth finds, as the result of many analyses, that 12 parts of the 

 non-fatty solids are thus made up on the average : 



Milk sugar 6 



Mineral matter, or ash ] 



Nitrogenous matter, or proteids 5 



12 



Of the nitrogenous matter rather more than two-thirds consists of 

 casein, the specific component part of cheese. From the foregoing 

 figures is calculated the following average percentage composition of 

 the non-fatty solids of milk : 



Milk sugar 50 



Mineral matter, or ash 8 



Nitrogenous matter, or proteids 41| 



100 



The average composition of all the milk received at the Aylesbury 

 Dairy Company's premises at Bayswater indicates a great uniformity 

 in the quantity of non-fatty solids, and a rather marked variation in 

 the percentages of fat, with, of course, a concomitant fluctuation in 

 the amount of total solids. Towards the end of the year more par- 

 ticularly in November the milk attains its highest quality, while in 

 the spring months the poorest milk is received, another diminution in 

 quality frequently occurring in July. Of these fluctuations Dr. Vieth 

 offers the following explanation : In autumn the majority of cows are 

 stale, and they then give a limited quantity of milk, which is of high 



