MAMMARY GLANDS 75 



The relative proportion of gland tissue and connective or 

 framework tissue is presumably a matter of heredity, except as 

 the udder is affected by injury or disease. 



Ability to digest large amounts of food material, the tendency 

 to dairy assimilation, the capacity for large flow of blood through 

 the udder, the tendency to a large number of gland cells within 

 the udder, and the tendency to relatively large proportion of 

 gland tissue as compared with the connective tissue are all mat- 

 ters of heredity, fixed by a long line of intelligent breeding. 



Mare's milk differs from cow's milk in possessing more water 

 and sugar and less fat, casein, albumin, and mineral matter. 

 Her udder differs from that of the cow in having but one gland 

 in each half. There are from two to four cisterns at the base 

 of the teat instead of one, and each cistern has an excretory 

 canal to the point of the teat. 



Here again we have the same general device which in effect 

 puts a thin sheet of moving blood as close as possible to a thin 

 sheet of epithelial cells supplying the latter with materials for 

 manufacture and with this, suitable devices for holding and dis- 

 posing of the product (in this case milk). 



A cow's udder may consist largely of gland tissue, with just 

 enough connective tissue to support it and hold shape ; it may 

 consist largely of connective tissue with a relatively smaller 

 amount of gland tissue. AVhat is the probable structure of the 

 udder that remains large and hard after milking? What are 

 some of the reasons why small udders may produce well and 

 large udders produce poorly? 



Note the large vein running from under the udder forward 

 under the belly. This is the abdominal subcutaneous vein pre- 

 viously mentioned ; it varies greatly in size and shape, and drains 

 the inguinal region, including the udder. What possible rela- 

 tion is there between the size of this vein and the milk-produc- 

 ing capacity of the udder? Why is a very large vein and a 

 large opening for it in the belly wall significant? 



What effect has unusual nerve excitement on the production 

 of milk? Explain this effect. 



Disorders. — Disorders of the udder may be of great impor- 

 tance even though slight and local. Garget may refer to an 

 unusual congestion or to a true inflammation (mammitis), in- 

 volving the mucous membrane of the milk ducts, alveoli, and 

 the connective tissue framework of the udder. Injuries to the 



