v.] CONNECTIVE TISSUE. 65 



C. Pigment-Cells. 



Pin out on a frog-board one of the webs between 

 the toes of the frog used in B. § 2, and observe 

 first under a low and then under a high power. 

 There will be seen large corpuscles loaded with 

 dark pigment, and possessing numerous branched 

 processes. In some places the pigmented cells 

 will appear as round dots, the processes in this 

 case having been retracted. Every intermediate 

 stage between these two states may be observed 

 by watching from time to time. 



E. Fat-Cells. 



1. Cut out a small piece of the omentum, from a 

 part containing comparatively little fat, Spread 

 it out on a slide and mount it in normal saline 

 solution. Observe 



a. Under a low power, the groups of highly 

 refractive fat-cells. 



b. Under a high power, the variable size of the 

 fat cells, the apparent absence of a nucleus, 

 the connective tissue passing between and 

 over the cells, 



2. Place a similar piece of omentum in osmic acid 

 1 p.c. for about half-an-hour, wash with water 

 and mount in dilute glycerine. Observe that 

 the fat-cells are stained a deep brown-black (cp. 

 Less. IV. § 5). If the tissue after washing be 

 placed in alcohol (preferably 75 p.c.) the tint will 

 become much darker. 



