GLANDS. 101 



of these oil-globules which, instead of being free and 

 solitary, are aggregated together in little round mass- 

 es, forming what are known as globules of colostrum 

 (fig. VI. 2). When the gland is in a state of inflam- 

 mation, these colostrum globules make their appear- 

 ance in the milk. The good quality of the milk is 

 known by the large number and equality in volume 

 of its globules. 



On reviewing and comparing the glands, whose Division of 

 structure we have thus far studied, reference being 

 had solely to the character and arrangement of their 

 epithelium, it is obvious that they can be divided 

 naturally, into two groups : 1st, glands with simple 

 epithelium ; 2d, glands with stratified epithelium. 

 In each of these varieties the process of secretion is 

 differently accomplished. In the first group, the 

 plasma of the blood exudes through the epithelial 

 layer, is modified by its cells, and passes out through 

 the excretory duct without carrying with it any solid 

 elements ; this is the process of secretion by -simple 

 filtration. In the second group, in which the epi- 

 thelial cells are packed in strata, the blood plasma, in 

 passing through them, excites in them a higher grade 

 of vital action ; they increase rapidly both in size and 

 number, and their contents undergo at the same time 

 a specific change ; but both the cells and their con- 

 tents ultimately become disaggregated, melt down, as 

 it were, and thus form the secretion which is hence 

 called secretion by epithelial growth. 

 ;\ The salivary glands, and the numerous family of 

 mucous follicles, effect their secretion by the mode 

 first described ; the sebaceous glands, and the mam- 



