692 Scientific Proceedings, Royal Dublin Society. 



The experiments of 1915 and 1916 suggested various explanations for the 

 peculiarities in the proportion of butter-fat in the morning and evening milk ; 

 and a supplementary experiment was performed in 1918. Two cows were 

 milked perfectly dry at each milking for six days ; for the succeeding five 

 clays the strippings were left with them at each milking ; and for another 

 six days after the cows were again milked dry. Samples were taken, and the 

 percentages of fat and solids determined in the usual way throughout the 

 period. Diagram II represents the morning and evening yields for cow 7, 

 diagram III the daily yield for cows 7 and 19 for the same time. From 

 diagram 111 it is evident that leaving the strippings tends in two or three 

 days to reduce the quantities of milk and of solids-not-fat ; but the reduction 

 is not so evident in the case of total fat. The effect on the morning and 

 evening yields (diagram II) is to decrease the. morning milk, solids-not-fat, 

 and fat, and either to increase or leave unchanged the evening milk, solids- 

 not-fat, and fat. This influence is more evident in the case of total fat than 

 in the other constituents. 



The strippings include the residue from the upper part of the gland ducts, 

 and the immediate secretion of the alveolar cells. The experiment suggests 

 that more fat remains in the same quantity of strippings after the morning 

 than after the evening milking. When a cow is milked dry there remain in 

 the alveolar cells substances which are either identical with the constituents 

 of milk, or are milk-precursors, and, probably, the quantity of these materials 

 is considerable. " The effect of an injection of pituitary extract is to cause 

 the immediate secretion of the milk (stored in the gland) which would other- 

 wise have been drawn off at the next milking. Thus by injecting after the 

 morning milking, a large portion of. the evening milk can be obtained at 

 once. The conclusion from this is that the milk constituents are stored in 

 the gland cells in the form of precursors ; for it is difficult to imagine that 

 these substances could be formed from the blood in the time, and in such 

 definite quantities." 1 Assuming that the gland works more or less uni- 

 formly throughout the day, one concludes that these substances are being 

 poured into the ducts continuously, the fats in suspension in the form of 

 globules, and the solids-not-fat in solution. When the ducts are filled, back 

 pressure on the alveolar cells is produced, and this acts in opposition to 

 their secreting action. Because of the globular condition of the fat, it is 

 more difficult for it to pass from the alveolar cells into the duets against 

 pressure than it is for the solids-not-fat and water ; and, consequently, at the 

 beginning of a milking there is a surplus store of fat globules nqt extruded 



1 Hammond : Quarterly Journal of Experimental Physiology, vol. vi, p. 315. 



