28 



VETERINARY PHYSIOLOGY 



the ends of which the fibres extend. In some of the loose 

 fibrous tissues they retain this shape, but in the denser tissues 

 they get squeezed upon, and are apt to be flattened and to 

 develop processes thrust out into the spaces. 



In certain situations, peculiar modifications of Fibroblasts 

 are to be found 



(A) Endothelium. When these cells line the larger connec- 

 tive tissue spaces they become flattened, and form a covering 

 membrane, called an endothelium. Such a layer lines all the 

 serous cavities of the body, and the lymphatics, blood vessels, 

 and heart, which are all primarily large connective tissue 

 spaces. To demonstrate the outlines of these cells it is neces- 



FIG. 10. Fat Culls stained with osmic acid, and lying alongside 

 a small blood vessel. 



fcary to stain with nitrate of silver, which has a special affinity 

 for the interstitial substance, and which thus forms a series 

 of black lines between the cells. 



(B) Fat Cells. In the areolar tissue of many parts of the 

 body fat makes its appearance in the cells round the smaller 

 blood vessels, and when these cells occur in masses Adipose 

 Tissue is produced. 



Little droplets of oil first appear, and these become larger, 

 run together, and finally form a large single globule, distending 

 the cell, and pushing to the sides the protoplasm and nucleus as 

 a sort of capsule (fig. 10). 



If the animal be starved, the fat gradually disappears out of 

 the cell, and in its place is left a clear albuminous fluid which 

 also disappears, and the cell resumes its former shape. 



