e ' c - 



six t. 21.] TISSUE OF GLANDS. 39 



The glands either separate certain constituents from the blood, 

 or prepare, by means of it, peculiar substances, Fig . )3 . 



or morphological elements ; and the importance 

 of their individual parts is different according 

 to circumstances. In the former case, the 

 gland-cells play rather a subordinate part, and 

 are of importance only in so far as they hinder 

 the passage of some constituents of the blood, 

 and allow certain others to pass through (kidneys, 

 lacrymal glands, small sudoriferous glands, 

 lungs) ; in the second case, on the other hand, 

 the cells play an essential part in the formation 

 of the secreted juice, as they produce the specific 

 secretion within themselves, which either tran- 

 sudes from them (liver, thyroid, mucous glands, 

 gastric glands, prostate, Cowper's glands, sali- 



■, -, N ii,i I.kbcrkUhnian gland of 



vary glands, pancreas), or escapes by detach- me pig; magnified sixty 



-. iii i- r ,i n times, a. Membrana pro- 



ment and gradual destruction of the cells pr ;a and epithelium, a. 

 (mammary and sebaceous glands, testicles, large w } ' 

 sudoriferous and ceruminous glands). In the latter case, new 

 elements constantly supply the place of the mature decaying 

 gland-cells, by which means the character of these cells, as a 

 lining of the gland canal, is frequently effaced, and they appear 

 as the secretion (testicles, mammary gland during lactation). All 

 the glands mentioned, with the exception of the sexual glands, are 

 developed from the internal and external epithelial formation of 

 the body, with the co-operation of the vascular membranes sup- 

 porting these cpithelia. Some of them appear from the com- 

 mencement as outgrowths of the membranes mentioned, and retain 

 their cavities during the whole course of their development (lungs, 

 small intestinal glands). Others are at first hollow, but subse- 

 quently have solid extensions, by means of which they are further 

 formed (liver) ; others, again, are solid from the commencement, 

 continue to grow in this condition, and then first acquire their 

 cavities (glands of the skin, racemose glands). The thyroid and 

 thymus also arise, according to Remak, as constrictions from the 

 intestinal epithelium. Molecular change is carried on with great 

 energy in glands, and they belong to the most vascular organs of 

 the body. Glandular tissue, except in the uterine glands, is never 

 regenerated; while, on the other hand, hypertrophies of it, and 

 even accidental formations of small glands, occur. 



The true glands of the human body may, according to the 



