The Variation of Milk Secretion with Age. 59 



therefore to consider the fit of this curve measured by a ^ 2 

 somewhat more than 17.00 or what would correspond to the 

 P of. a very good fit. 



The equation of the curve has many practical uses aside 

 from its interest in a scientific sense. By its use the records of 

 cows at different ages may be brought to the same basis for 

 comparison whether it be for milk inheritance studies, analysis 

 of judging experiments or the like. The time of the theoretical 

 maximum of milk production may be easily calculated from it 

 by differentiation. This maximum is shown to be 7 years 2.4 

 months a figure considerably above the age customarily called 

 mature form. Further the curve shows that the method used in 

 advanced registry work of determining the amount a Jersey 

 cow should produce for the Register of Merit is falacious in 

 that it is a linear method and does not recognize this logarithmic 

 nature of milk production. In a previous paper the average fat 

 per cent of Jersey cows is given as 5.12. Assuming this figure 

 and dividing the pounds of butter-fat by it gives us the average 

 requirement for milk production in one year. Supposing that 

 Y\ of the year's records is made in the first 8 months of lacta- 

 tion (a figure reasonably close to the expected (Pearl- 191 5) the 

 required production is found to be 3600 pounds at 2 years and 

 5200 pounds at 5 years. 



Causally considered the logarithmic nature of milk produc- 

 tion is of a good deal of interest. The work of a number of 

 students of growth, beginning with Minot's notable studies on 

 rabbits have shown that the phenomena of growth is also a 

 logarithmic function of age. This law appears of wide general 

 application as the work of Lewenz and Pearson have shown it 

 holds for growth in children ; Donaldson, Hatai and Jackson 

 have shown it is of general application to the growth of certain 

 organs in the white rat and Pearl and Surface have shown it 

 true for ceratophyllum and corn. It seems, therefore, altogether 

 likely that the mammary glands of the cow also follows this 

 rule. Should this prove true the increase of milk production 

 with age seems of much significance in paralleling these growth 

 phenomena. This paralleling of the two functions would, in 

 fact, seem to indicate causal relation between the two in that 

 the increase in milk production may depend chiefly on the in- 

 crease in actual mass of the mammary gland due to growth of 



