SheeHy — Variation in the Quantity and Quality of Coios 1 Milk. 587 



To explain some of the results of the 1915 and 1916 experiments, 1 con- 

 ducted by the writer at the Albert Agricultural College, supplemental 

 experiments were started in 1918. The milk from each teat of an individual 

 cow was sampled at three stages of the milking, namely, when the operation 

 started, when about half the milk was drawn from the udder, and, finally, 

 when nothing was left in the udder except the amount of the sample. 

 Thus twelve samples of about half a pint each were taken at each milkin°-, 

 and from these the percentage of fat and the specific gravity were determined. 

 The percentages of solids and of solids-not-fat were then calculated. 

 Table I contains the accumulated data from cow 23 and cow 15. At the 

 beginning of the milking the half pint sample of the first — " fore " in table — 

 milk was drawn from each teat separately in the order from left to right on 

 the table. All the teats were then milked in the normal fashion till the cow 

 had given about half the expected quantity, when the teats were again 

 milked in the same order into the sample bottles. This sample is labelled 

 " middle " on the table. Milking was again proceeded with till only approxi- 

 mately half a pint was left in each quarter of the udder ; then the teats were 

 again emptied in the same order into the third set of sample bottles — last 

 on table. The percentages of fat and of solids-not-fat in the fore, middle, 

 and last samples from each of three milkings of cow 23 are represented in 

 diagram I. From the table and diagram it is evident that, as the operation 

 of milking proceeds, the milk yielded gives a percentage of fat which in- 

 creases from the " fore " milk up to the " strappings," and a percentage of 

 solids-not-fat, which decreases : that is, the percentage of fat is much higher, 

 and that of solids-not-fat lower in the strippings than in the first milk. 



The alveolar cells of the mammary gland pour out their secretion into the 

 ducts or canals which lead to the little milk reservoirs where the material 

 is stored. It has been calculated that the udders of cows could not contain 

 all the milk which is sometimes drawn at one milking, so that secretion 

 must be proceeding at the same time. 2 Lehman 3 injected sulphindigotate 

 of soda solution into a vein of a milch goat ; and, on milking the animal 

 immediately afterwards, found a blue tinge in the strippings. A considerable 

 quantity of the fluid drawn at a milking is, therefore, secreted during the 

 process of milking. That secretion proceeds during milking in a lactating 

 eat is shown conclusively by the experiments of Jackson and Eothera, 4 where 

 29-47 per cent, of the milk was produced in the short period during which 

 the kittens were sucking the mother. 



1 Sheehy : Soient. Proo. Royal Dublin Society, vol. xv, 1919, pp. 546 and 574. 

 2 Schafer: "Text Book of Physiology." vol. i, p. 663. 

 3 Ibid. i Biochemical Journal, viii, 1914. 



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