98 Fluid obtained from. Udders of Virgin Heifers 



undergoes a cycle correlated with that existing in the ovaries and 

 culminating at oestrus by a swelling of the mammary gland. Since 

 heifers have periodic corpora lutea and a well-marked ovarian cycle, 

 it might be supposed that the former acted in much the same way as 

 those of pseudo-pregnant rabbits, but to a smaller extent. It was not 

 unreasonable therefore to suppose that this Ouid was secreted just before 

 the period of oestrus in heifers, but attempts to prove this so far have 

 been without success. The fluid can be drawn off from tlie udder at any 

 period of the cycle, and the amount varies considerably according to 

 the individual. In animals killed at various periods of the oestrous cycle, 

 there was an indication that more existed just before the oestrous period 

 than at any other time. But individual cases were also found which did 

 not show this behaviour. 



The secretion of milk has been attributed to the removal of the 

 stimulus which caused the mammary gland to develop. Thus Lane- 

 Claypon and Starling (-5) and others have attributed this action to the 

 foetus, but Marshall and Hammond (2) found that the corpus luteuni 

 caused the growth of the mammary gland in the rabbit, and that milk 

 was produced whenever the gland had developed to a sufhcient extent. 



The removal of the causative stimulus in heifers cannot, however, 

 be the cause of the secretion, as the fluid has been found in the udders 

 of previously virgin heifers pregnant 'i-A montlis, at a time when the 

 corpus luteum is still large and active. 



The problem thus presented itself: Is the secretion similar to that of 

 colostrum and milk, resulting from the activity of the cells of the alveoh, 

 or is it merely an exudation of lymph filling up the galactophorous 

 sinuses, which have been formed by the development of the mammary 

 gland? If the latter hypothesis be found correct, then at what stage 

 in the development of the mammary gland do the typical constituents 

 of milk first appear? 



Chemical investigation of the fluid. 



In all, four samples of the fluid were examined. The first two samples 

 were obtained from heifers which had never been served, whilst the 

 third and fourth samples were taken from the udders of the heifers 

 during the first three weeks of pregnancy. 



The amount of fluid was only small, ea(^h heifer contributing on an 

 average about 7 c.c. to the supply. The liquid was slightly opaque in 

 appearance, though not possessing the dense opaqueness of milk. A 

 slight sediment settled out on standing, but the fluid passed fairly 



