10 Proceedings of the Royal Society of Edinburgh. [Sess. 
nutrition and growth, as compared with those whose mothers are on a 
bread-and-milk diet. 
Whether this is due to a mere deficiency in the amount of milk avail- 
able for their use, or to some alteration in its constituents, has not been 
determined, but the probability is that the former plays a large part. 
On microscopic examination there are no marked differences in the 
histological characters of the mammary tissues. The character of the 
glandular tissue varies according as the acini are full of secretion or empty, 
and while the mammge of the meat-fed animals show a preponderance of 
closely packed empty lobules, this may only be due to the fact that the 
mothers had been killed shortly after the gland had been emptied by 
suckling. 
Conclusions. 
1. That a meat diet is prejudicial to the occurrence of pregnancy in 
rats. 
2. That in rats fed on a meat diet the mammary development of 
nursing mothers is less than in rats fed on bread-and-milk.* 
* The expenses of this investigation were defrayed by grants from the Moray Fund of 
the University, and from the Carnegie Trust. 
(Issued separately February 11, 1907.) 
