04 ANIMAL PHYSIOLOGY. [LESSON 22. 



be distinctly traced to the spontaneous division of the nucleus, as in 

 plants. 



374. A good example of this fact is met with in the develop- 



ment of Cartilage ; if we examine young 

 Cartilage (or the Cartilage of young 

 animals), where the tissue is in a state 

 of active formation, groups of cells will 

 be found, the nucleus sometimes entire, 

 sometimes just divided, and other ex- 

 amples in which division and subdivision 

 (into four parts) have taken place (Fig. 

 91) ; the primary cells (a) contain an 

 entire nucleus; the secondary cells (b) 



-- " show the division into four nucleoli, 

 while the remainder of the cells sim- 

 ply demonstrate division. 



SIMPLE FIBROUS TISSUES. 



375. All animals possess a very large amount of what has been 

 improperly called Cellular tissue ; this term is now restricted, how- 

 ever, to those tissues which are found to consist of a congeries of 

 cells, and the word Areolar has been proposed (and adopted) in place 

 of Cellular tissue. 



Examined by the microscope this tissue is found to consist of a 

 net-work of minute fibres and bands, interwoven in every possible 

 directipn, leaving innumerable interspaces communicating with each 

 other. When a butcher kills a calf, he makes a small hole in the 

 skin, applies his mouth, and blows into it ; by this means he distends 

 the whole body, because he has inflated the areolar tissue. If the 

 human body, the body of a dog, or of any other animal, be allowed to 

 remain in the water after death, gas is generated as the result of in- 

 cipient decomposition ; it fills the meshes of the areolar tissue, and 

 distends the body enormously ; as a consequence of its great buoy- 

 ancy it is enabled to float on the surface of the water. 



376. The fibres which enter into the composition of Areolar tis- 

 sue, designate two other distinct tissues, i. e., the white fibrous and 

 the yellow fibrous tissues,' both of these have an independent exist- 

 ence, however, in other parts of the body. 



377. Thus the white fibrous tissue exists alone in Ligaments, 

 Tendons, Fibrous Membranes, &c., where it presents precisely the 



