I2O HOW TO WORK 



cells which can be found, should be subjected to examination as an 

 opaque object. 



The mesentery, or fold of delicate membrane which attaches the 

 intestine to the spine, of small animals, is the best place for obtaining 

 good specimens of adipose tissue, and being protected by the trans- 

 parent covering, the relations and form of the fat vesicles are not 

 altered. In this situation, too, the nucleus of the vesicle may often 

 be demonstrated, and cells in every stage of growth can easily be 

 found. Such a preparation, the vessels of which have been previously 

 injected with Prussian blue fluid, will afford an opportunity of 

 demonstrating all peculiarities of adipose tissue. Near the ovary 

 of the newt and many other batrachia, there exist small collections 

 of adipose tissue. The vesicles are much shrunken during the spring, 

 when the ova are increasing in size, and at this time the nucleus is 

 beautifully distinct in each vesicle. The nuclei of the cells may also 

 be seen very distinctly, especially in starved fat cells, after treatment 

 with a little acetic acid, pi. XXVII, fig. 172. Ordinary adipose 

 tissue with connective tissue containing much of the yellow element 

 is represented in pi. XXVII, fig. 174. 



Frequently the more solid portion of the fat will crystallise on 

 the surface of the more oily, in small acicular crystals, which radiate 

 from a centre forming a star-like mass, as seen in the figures 172, 173. 

 Adipose tissue should be examined by low as well as by high 

 powers (a two inch, or an inch, and a quarter of an inch object- 

 glass), and by reflected as well as transmitted light. 



217. Cartilage. The characters of cartilage are very easily de- 

 monstrated. A thin section may be placed in water or glycerine. 

 Specimens should be taken from the larynx, trachea, the ear, the ribs, 

 the articular cartilage of joints, and the fibro-cartilage between the 

 vertebras, and in other situations. The ear of the mouse affords the 

 best example of cartilage consisting almost entirely of cells. The 

 thin layer in the upper portion of the cartilage is very favourable for 

 studying the nutrition and mode of growth of the cells, the intercel- 

 lular substance or matrix being very small in quantity in this variety 

 of membraniform cartilage. Specimens of cartilage keep very well in 

 dilute spirit and water, creosote fluid, and many other solutions, but 

 on the whole glycerine is to be preferred as the medium for their pre- 

 servation. 



The development of cartilage, and the changes by which it is 

 converted into bone, may be successfully studied in the flat bones of 

 the skull of a small frog. The general changes occurring in the 

 growth of cartilage will be understood by reference to pi. XXVII, 

 fi!>s, 175, 176, 177, 178, " On the formation of the so-called inter- 



