LACTATION' 



607 



the entire surface is found to IK? covered with a layer of glandular 

 tissue, the margins of the individual glands being practically 

 contiguous, each of them having a diameter of from five to eight 

 centimetres. Sections show that the formation of alveoli (/./. definite 

 secretory structures) has begun at this period, especially at tin- 

 periphery, where the gland is generally somewhat tjiicker than in 

 other parts. 



From this stage onwards the growth of the ducts and the 

 formation of alveoli proceed rapidly, so that by the twenty-fifth 



FIG. 167. Section of mammary gland (human), showing d<-\ rlopinjr a l\ t -oli. 

 (From Sharpey Schafer, after von Ebnt-i .) 



/>, Connective tissue ; <7, undeveloped alveoli ; /', partially dr\ rl..]M- ( | 

 alveoli ; </, blood-vessel ; rn, portion of duct. 



of pregnancy the whole surface of the abdomen ha.- become covered 

 by mammary gland tissue, which may he half a centimetre thick. 

 This tissue is seen in sections to consist for the most part of alveoli, 

 in the cells of which fat glohules are in process of formation. 



From about the ninth day onwards to the twenty-fifth it is usually 

 possible to squeeze a watery fluid from the nipples. During the last 

 days of pregnancy this fluid assumes the characteristics of normal 

 milk, so that by the time of parturition, which occurs in the rabbit 

 on the thirtieth day after conception, the glands are full of milk. 



The multiparous rabbit differs from the virgin in possessing 

 ready-formed alveoli at the l>eginning of pregnancy. Consequently 



