212 Maine Agricultural Experiment Station. 1918. 



the determination of the concentration of either solid and selec- 

 tion of the animals accordingly will result in a corresponding 

 increase for the other solid. 



Taken in conjunction with the above results the diurnal 

 variations of cow's milk furnish the facts necessary to test the 

 hypothesis to account for the mode of secretion of the milk 

 solids. The data show that evening milk is between 0.678 and 

 0.723 per cent higher in butter-fat than the morning milk 

 throughout the whole lactation. Xo appreciable difference oc- 

 curs in the solids-not-fat. 



For the clear understanding of the bearing of these data 

 on the hypothesis to account for the mechanical mechanism by 

 which the solids are released into the milk, it seems best to 

 restate them in as simple terms as possible. These hypothesis 

 may be placed in 3 groups : 



A. The mammary gland cells break loose bodily and dis- 

 integrate in the alveoli. 



B. The portion of the cells toward the alveoli become 

 loaded with solids, break loose from the basal portion and dis- 

 integrate to form the milk solids. 



C. The cells of the mammary gland secrete the materials 

 of milk solids without themselves breaking down. 



These data offer citeria between the theories to account for 

 the secretion of the milk solids. On the cell disintegration the-! 

 ories the cell must contain a fixed quantity of solids-not-fat 

 while the butter- fat varies so that in the longer interval between 

 milkings the cell accumulates less fat than in the shorter time, 

 or taken the other way, the cell contains relatively more protein 

 and sugar than fat as the interval between milkings lengthens. 

 This is contrary to our knowledge of fat formation for it is 

 commonly accepted that first comes the cells composed largely 

 of protoplasm and that as time goes on this cell is more and 

 more loaded with fat at the expense of the protoplasm. Unless 

 these mammary cells behave very differently in the formation 

 of this fat than other body cells this variation is enough to seri- 

 ously discredit the hypothesis of cell disintegration to account 

 for these milk solids and in fact, to make it an absurdity. Fur- 

 thermore, as far as our knowledge of the variations of secretory 



