648 
Journal of Agricultural Research 
Vol. XI, No. 
correctly as representing the influence of the number of lactation periode 
upon the average percentage of fat for each period. The differencs 
between the results presented in this form and the actual influence of 
age upon the percentage of fat did not present the probability of being 
5.1- 
4.9- 
47 
- PER CENT COWS 
- PER CENT FAT 
74 COWS 
&3r 
5.1 _ 
4*9- 
4*7 
59 COWS 
j———■ 1 
S.3r 
5.1 
4£h 
<4*7 
45 COWS 
40 
20 
0 
60 
40 
20 
0 
60 
440 
J20 M 
* 
0 2 
Fig. i.—G raphs of the variation in percentage of fat of Jersey cows in successive lactation periods, and 
proportion of total number of cows in each group showing highest test in each period. 
of sufficient magnitude to justify the calculation of the data on the basis 
of the actual age of the animals. 
Although the dairy herd from whose records our data are drawn 
comprised animals of the four breeds already mentioned, not enough 
animals of the Shorthorn breed were included to warrant the use of 
