CONNECTIVE TISSUE. 27 



EXAMINATION (L and H). Observe the nearly continuous layer of endothelium in the 

 case of the young rabbit (PI. V., Fig. i) on each surface of the omentum (p. 26), the more 

 fenestrated character in the adult rabbit, and the almost net-like condition in the cat (PI. V., 

 Fig. 2). In all cases the silver lines, indicating the existence of the endothelium covering 

 the trabeculae, are seen. Focus down through one of the larger trabeculae, inside which con- 

 nective-tissue corpuscles may be found. Do not confound the large oval nuclei of the squames 

 which are always on the surface with the nuclei of the connective-tissue corpuscles proper. 

 Omit at present the study of the blood-vessels and the fat cells which frequently accompany 

 them. 



The omentum of a young rabbit is particularly valuable for studying the development of 

 fat-cells and blood-vessels. 



ADIPOSE TISSUE. 



This consists of small vesicles or cells filled with fatty substances. The cells are imbedded 

 in a small quantity of areolar tissue containing blood-vessels. Each cell has a distinct en- 

 velope, and contains a globule of clear, sometimes slightly yellow-coloured fat, which nearly 

 fills the cell, so that the nucleus, with a small amount of protoplasm surrounding it, is pushed 

 to one side and compressed against the cell-wall. .Study fully formed cells and fat-cells 

 developing. 



PREPARATION. Snip off a small piece of fat and tease it in a drop of salt solution on a 

 slide. Place a piece of paper between the slide and cover-glass, to prevent the latter pressing 

 on and rupturing the envelopes of the cells. 



EXAMINATION (L and H). Observe the relatively large size (^ - J^) of the clear, highly 

 refractive vesicles, sometimes compressed against each other. Usually no nucleus is visible- 

 If the cells have been ruptured, globules of fat of various sizes will be found floating about. 

 Irrigate with magenta solution (p. xliv), which stains the nuclei of the cells. They are seen 

 as small oval red spots compressed against the cell-envelope. Substitute glycerine for the 

 magenta, and mount for preservation. (Indicate this in PI. V., Fig. 4.) 



Effect of Osmic Acid. A similar preparation, without the magenta, may be irrigated with 

 a one per cent, solution of osmic acid, which blackens fatty matter, and hence is a most valuable 

 reagent for its detection. 



Examine the omentum of the cat (p. 26) and the preparations of areolar tissue (p. 22) 

 for fat-cells. 



Crystals of Margarine. Delicate, needle-shaped crystals, springing from a point within the 

 fat-cells, often occur. They are post-mortem appearances for the contents of fat-cells are 

 fluid during life and may readily be produced by steeping a morsel of fat for twenty-four 

 hours in glycerine, or long steeping in alcohol, or after partial digestion (p. 92). 



The Envelope of Fat Cells is easily shown by steeping a morsel of fat in ether, which dis- 

 solves out the fat and leaves the empty shrivelled-up envelopes. (Indicate this in PI. V. 

 Fig- 5.) 



DEVELOPMENT OF FAT-CELLS. 



PREPARATION. Place a small piece of the skin of a foetus in rectified spirit for three 

 days. At the end of that time, make vertical sections in the ordinary way by freezing. 

 After the gum has been removed from them by steeping in water, place some of them in a 



