DAIRY FABMIXG DAIEYI17G. 877 



The author concludes that " after allowance has been made for the varying 

 age and duration of the lactation period of the Ayrshire cows under examina- 

 tion, the milk of cows which gave the larger average weekly yields of milk 

 shows a definite and appreciable tendency to be poorer in milk fat than the 

 milk of cows which gave lower average weekly yields. The duration of lacta- 

 tion, had no significant influence upon the average percentage of milk fat 

 produced. 



" The percentage of milk fat showed a slight, but definite, tendency to be 

 lower in the older than in the younger cows, after due allowance has been made 

 for the average weekly yield of milk. Taking the herd as a whole, the duration 

 of the lactation bore no relation to the average weekly yield of milk produced 

 by the cows. There is thus no evidence, in the Fenvdck herds, of a selective 

 action in favor of retaining in milk those cows that gave a better average yield 

 of milk than others. In the herd under examination, the older cows show a 

 definite and appreciable tendency to give larger yields of mUk than the younger 

 cows. This may possibly be due partly to a selective action in weeding out 

 cows which proved unpromising as regards their milk yield when young, and 

 partly to a physiological tendency for older cows to give better yields than 

 younger ones. To what extent, however, the tendency may be due to selective 

 or to phj^siological causes, the coefficient, as it stands, does not permit of 

 determination. The duration of lactation has possibly tended to be longer in 

 older than in younger cows. On this point, however, the evidence is not quite 

 definite. The existence of such a tendency might be due to selective action in 

 weeding out from the herd those cows whose lactation was rather short, or to 

 physiological causes, tending to extend the duration of lactation in older cows. 

 The value of the coefficient, however, makes it doubtful whether either tendency 

 really exists." 



The regression equation, representing the most probable value of a deviation 

 from the mean percentage of fat in terms of deviations from the means of the 

 other variables, is: .«i= — 0.022 a?2+0.002 Xs — 0.018 Xt, in wiiich Xi=Si deviation 

 from the average percentage of milk fat; iC2=a deviation from the average 

 weekly yield ; a?3=a deviation from the average duration of lactation ; and a?4= 

 a deviation from the average age of cows. From this it is possible in practical 

 use to determine the approximate relation that is to be expected between milk 

 yield and percentage of milk fat when either of these factors are increased or 

 diminished. However, the author explains that " while this result may be 

 regarded as the most probable, in the long run the certainty of attaining it 

 diminishes when only a small number of cows is being dealt vdth, and increases 

 proportionately with the number of cows in the herd in which the policy of 

 selecting cows with higher milk yields is pursued." 



On the effect of the neutralization of a culture medium with chalk on the 

 activities of the sour milk bacteria, J. A. Makeinoff {Centbl. Bakt. [etc.'\, 

 2. AM., 87 {WIS), No. 22-25, pp. 609-622) .—After outlining the work of pre\'ious 

 investigators the author discusses investigations conducted to determine the 

 amount of acid produced and the time required to produce sour milk under 

 neutraWzed conditions. It was found that chalk is a suitable neutralizer. 



Milk hygiene, W. Ernst {Grundriss der Milchhygiene fiir Tierdrztc. Stutt- 

 gart, 1913, pp. VIII+301, pis. 5, figs. 26). — This is a treatise on milk hygiene, 

 including chapters on the anatomy and pathology of the milk gland; the 

 physiology of lactation ; the microscopical characteristics of milk ; the composi- 

 tion of milk and its biological, chemical, and physical characteristics; internal 

 influences on the character of milk ; bacteria ; and milk control and investi- 

 gation. 



