Sheehy — Variation in the Quantity and Quality of Coivs* Milk. 589 



The figures for the proportion of solids -not-fat indicate that the con- 

 centration of some or ail of the components increases while the milk is 

 resting in the udder. That is to say: diffusion must take place through 

 the walls of the gland tubules. The proteids of milk are not diffusible : con- 

 sequently the possibility of diffusion is confined to the sugars, salts, and water. 

 That sugars can be and are re-absorbed is suggested by the fact that lactose 1 

 is found in the blood of mammals immediately after parturition. If the 

 " strippings " be taken to contain the percentage of solids-not-fat in milk as 

 it is poured out by the alveolar cells, and .the fore milk, which contains a 

 higher percentage of solids-not-fat, be considered as that which has been 

 lying in the reservoir of the udder for several hours, re-absorption of water 

 must take place. A. similar theory of concentration of salts in the urine 

 has been foimulated by Carl Ludwig, 2 in which he states that the salts 

 poured through Bowman's capsule in the Malpighian bodies of the kidney 

 are concentrated along the uriniferous tubules. Fat, in the globular form, 

 as it exists in milk, is not diffusible. This, combined with the fact that the 

 percentage of fat is much higher in the strippings than in the first milk, 

 suggests that the percentage of fat in the strippings is not similar to that in 

 the milk liberated from the alveolar cells at other times. 



In the above experiment the order in which the teats were milked was 

 successively changed, as the investigation proceeded. No definite effect was 

 produced by this procedure : the four quarters, which are anatomically 

 distinct from one another, give milk which differs in the proportion of both 

 fat and solids-not-fat. A peculiar feature is the inconsistency of the yield of 

 any parr-, both in solids-not-fat and butter- fat; there is some variation in the 

 successive yields of any individual quarter, showing that the glands therein 

 are not constant in action. Histological examination also shows that while 

 the gland is actively at- work there may be some alveoli inactive for the time 

 being ; and chemical examination suggests different composition 3 for 

 different parts of the mammary gland. A pail of milk drawn from a cow is, 

 therefore, a. compound product ; it is the sum of the products of four separate 

 and different quarters, 4 in each of which the activities of the neighbouring 

 alveoli probably differ. 



1 " Compt. rend. Acad. Sci.," vol.. cxxviii, 1904. "Arch. f. wiss. u. prakt. Tierheilk," 

 vol. xxxv, 1904. Marsh: " Physiology of Reproduction," 1910. 



2 Halliburton's " Physiology," 1913, p. 577. 



3 " The Chemistry of the Mammary Gland," J. A. Campbell: Quarterly Journal 

 of Experimental Physiology, vol. vii, p. 53. 



4 " Variation in the Composition of Cows' Milk," •Crowther : Journal of Agri. 

 Science, vol. i, p. 171. 



