314 SECRETION. 



2. Follicular glands. Examples of these are the simple mucous follicles, 

 the follicles of Lieberkiihn and the uterine follicles. 



3. Tubular glands. Examples of these are the ceruminous glands, the 

 sudoriparous glands and the kidneys. 



4. Racemose glands, simple and compound. Examples of the simple 

 racemose glands are the sebaceous and Meibomian glands, the tracheal 

 glands and the glands of Brunner. Examples of the compound racemose 

 glands are the salivary glands, the pancreas, the lachrymal glands and the 

 mammary glands. 



5. Ductless, or blood-glands. Examples of these are the thymus, the 

 thyroid, the suprarenal capsules and the spleen. 



The liver is a glandular organ which can not be placed in any one of the 

 above divisions. The lymphatic glands and other parts connected with the 

 lymphatic and the lacteal system are not true glandular organs ; and these 

 are sometimes called conglobate glands. 



The general structure of secreting membranes and of the follicular 

 glands is very simple. The secreting parts consist of a membrane, gen- 

 erally homogeneous, covered on the secreting surface with epithelial cells. 

 Beneath this membrane, ramify the blood-vessels which furnish materials 

 for the secretions. The follicular glands are simply digital inversions of 

 this structure, with rounded, blind extremities, the epithelium lining the fol- 

 licles. 



The tubular glands have essentially the same structure as the follicles, 

 except that the tubes are long and are more or less convoluted. The more 

 complex of these organs contain connective tissue, blood-vessels, nerves and 

 lymphatics. 



The compound racemose glands are composed of branching ducts, around 

 the extremities of which are arranged collections of rounded follicles, like 

 bunches of grapes. In addition to the epithelium, basement-membrane and 

 blood-vessels, these organs contain connective tissue, lymphatics, non-striated 

 muscular fibres, and nerves. In the simple racemose glands the excretory 

 duct does not branch. 



The ductless glands contain blood-vessels, lymphatics, nerves, sometimes 

 non-striated muscular fibres, and a peculiar structure called pulp, which is 

 composed of fluid with cells and occasionally with closed vesicles. These 

 are sometimes called blood-glands, because they are supposed to modify the 

 blood as it passes through their substance. 



The testicles and the ovaries are not simply glandular organs ; for in 

 addition to the production of mucous or watery secretions, their principal 

 office is to develop certain anatomical elements, the spermatozoids and the 

 ova. The physiology of these organs will be considered in connection with 

 the physiology of generation. 



Classification of the Secreted Fluids! The products of the various glands 

 may be divided, according to their uses, into secretions proper and excretions. 

 Some of the true secretions have certain mechanical uses, and some, like 

 mucus, are thrown off in small quantity without being actually excremen- 



