STKUCTUBB OF GLANDS. 



609 



a process of "duplicative subdivision" analogous to that by 

 VFliich the multiplication of cells takes place in the Vegetable 

 Kingdom (Fig. 67). The substance of these cellular Cartilages 

 is entirely destitute of blood- 

 vessels ; being nourished F'g- 324. 

 solely by imbibition from 



FiQ. 3-23. 



/ 



<o 



A 



Fig. 323. Cellular CurtiUige of Mouse's ear. 



Fig. 324. Section of the brancliial CartiUige of Tadpole : — a, group of four cells, separating from 

 each otlier ; &, pair of cells in apposition j c, c, nuclei of cartilage-cells ; d, cavity containing three 

 cells. 



the blood brought to the membrane covering their surface. 

 Hence they may be compared, in regard to their grade of organi- 

 zation, with the larger Algse; which consist, like them, of aggre- 

 gations of cells held together by intercellular substance, without 

 vessels of any kind, and are nourished by imbibition through 

 their whole surface. There are many cases, however, in which 

 the structureless intercellular substance is replaced hj bundles 

 of fibres, sometimes elastic, but more commonly non-elastic ; such 

 combinations, which are termed yiSro-cartilages, are interposed in 

 certain joints, wherein tension as well as pressure has to be re- 

 sisted, as, for example, between the vertebrae of the spinal column, 

 and the bones of the pelvis. In examining the structure of Car- 

 tilage, nothing more is necessary than to make very thin sections 

 with a sharp razor or scalpel, or with a Valentin's knife (§ 106), 

 or, if the specimen be large and dense (as the cartilage of the 

 ribs), with the section-instrument (§ 107). These sections may 

 be mounted in weak spirit, in Goadby's solution, or in glycerine ; 

 but in whatever way they are mounted, they undergo a gradual 

 change by the lapse of time, which renders them less fit to dis- 

 play the characteristic features of their structure. 



424. Structure of Glands. — The various secretions of the body 

 (as the saliva, bile, urine, &c.) are formed by the instrumentality 

 of organs termed Glands ; which are, for the most part, formed 

 on one fundamental type, whatever be the nature of their pro- 

 duct. The simplest idea of a gland is that which we gain from 

 an examination of the "follicles" or little bags imbedded in the 

 wall of the stomach ; some of which secrete mucus for the pro- 

 tection of its surface, and others gastric juice. These little bags 

 are filled with cells of a spheroidal form, which may be consi- 



39 



