$6 NORMAL HISTOLOGY. 



axilla or groin of a foetal animal, such as a pig, 5 inches 

 long should be immersed for twenty-four hours in one-per- 

 cent, osmic acid ; then washed and teased, and mounted in 

 glycerin slightly tinged with eosin. The larger and 

 smaller fat droplets within the cells will be black, and 

 numerous cells will be seen in which the fatty infiltra- 

 tion has not commenced. 



To study the fat cells at a later period of development, 

 thin sections may be made from the subcutaneous fat of 

 the human foetus, at from six to eight months, or from 

 any mammal of corresponding age. These are stained 

 double and mounted in balsam. At this period, while 

 the fat droplet in many parts occupies the greater part 

 of the cell, a distinct crescentic mass of protoplasm is 

 still seen at one side, enclosing the nucleus. 



Section of Adult Fat Tissue. A small piece of subcu- 

 taneous fat from man should be hardened in alcohol, by 

 which the fat will be for the most part dissolved out of 

 the cells. Thin sections are made, stained double, and 

 mounted in balsam. This preparation shows the relation 

 of the cells to one another, and the lobular structure of 

 the tissue. If the blood-vessels of the part from which 

 the tissue is taken have been previously injected with the 

 blue gelatin mixture, the relations of the vessels to the 

 lobules and cells will be well shown. 



RETICULAR CONNECTIVE TISSUE. 



This tissue forms a large part of the supporting 

 framework of the lymphatic nodes, and is found, in 

 somewhat modified form, in other parts of the body. 

 It consists of delicate fibres, of varying diameter, 



