428 



the percentage of fat in the milk increased with tlie advance of the 

 period of lactation, and that in some cases this increase was iiaitic- 

 ularly marked toward the close of the period. No increase in the ]>cr- 

 centage of fat was noticed when the cows were turned to pasture in tlie 

 spring. Pre^^ous observations by the author, extending over 10 years, 

 on herds of cows in Mecklenburg showed that in general for several 

 weeks after going to pasture there was a very considerable increase in 

 the percentage of fat in the milk. The author believes that the absence 

 of an increase in tliis case can not be due to the cliaracter of the pas- 

 tiue, as it was of a far better quality than that on which the observations 

 in Mecklenburg were made. The only explanation which he is able to 

 ofier is that in the case of the Mecklenburg cows a considerably larger 

 amount of digesti])lc nutrients was consumed daily immediately after 

 being turned to pasture than had been consumed during the stall feed- 

 ing preceding it. lie believes this could not liavebeen true in the case 

 of the cows in the ]>resent investigation. 



The percentage of solids not-fat showed no very nuirked variations, 

 but in the case of .several cows the percentage was lower in the middle 

 than at the beginning or end of the lactation. The line showing the 

 monthly variations in the i>ercentage of solids very closely follows all 

 the deviations of that for fat. 



With the exception of - cows, the pemniiim- ot" solids and of fat 

 increased with the advance of the i)eriod of lactation. In the case of 2 

 cows, one 12 years old and the other of inferior value for milking 

 purp(»ses, the percentage of solids showed very little variation from 

 beginning to end of the ])eriod. The line showing the changes in the 

 percentage of fat in the total solids of the milk is of especial interest. 

 With regaid to the factors governing this percentage, three conditions 

 are conc«'ivable: (1) An in«'rease in the solids-not-fat proportional to 

 the increase in the fat, /. f. the milk retaining its relative tat content 

 and l»ec(»ndng ttnly absolutely richer in fat with the advance of the 

 period; (2) a relatively greater increase in the solids-not-fat than in 

 the fat, /. c. the milk beconung absolutely richer but relatively poorer 

 in fat with the advance of the period; (.'?) a ndatively smaller increase 

 in the percentage of solids not-fat than in that of fat, i. e. the milk 

 becoming not <mly absolutely but also relatively richer in fat. With 

 the single exception of the 12-yearold cow, the line showing the 

 peicciitage of fat in the solids shows a greater «u* less increa>se from 

 the beginning to tlu' end of the period, that is the milk of the cows 

 under trial became both relatively and absolutely richer in fat with the 

 ad\ ance of the i>eriod. While the total activity of tii(» milk glands 

 decreased more and more with the a<lvance of lactation, that part of t he 

 energy devoted to the secretion of the fat decreased i>roportionally 

 slowest of all, that is the secretion of fat decreased more slowly than 

 that of the albuminoids, milk sugar, mineral salts, etc. 



