LABORATORY DIRECTIONS. 465 



Prepare endothelium as follows: 



(1) Kill a small animal, as a rat. 



(2) Open abdominal cavity. 



(3) Wash out cavity with sterile water; do not 



handle the mesentery. 



(4) Fill cavity with per cent, silver nitrate 



solution, 5 min. See that mesentery is 

 bathed. 



(5) Wash cavity with \ per cent, nitric acid 



solution, 5 min. 



(6) Fill cavity with alcohol 95 per cent, one-half 



to one hour, as convenient. 



(7) Remove mesentery with intestine attached. 



(8) Immerse in fresh 95 per cent, alcohol one to 



twelve hours. 



(9) Cut intestine away from mesentery and im- 



merse the latter in fresh 95 per cent, alcohol, 

 one-half to one hour. 



(10) Transfer mesentery to clove oil and expose 

 to sunlight in shallow wide dish, three to five 

 hours. Direct sunlight is not good. 



(n) Cut mesentery into small pieces and mount 

 in balsam. Handle mesentery as little as 

 possible during the whole process. 



Glands. 



i. For simple mucous and serous glands make 

 cross sections of the skin of a salamander. 



Connective Tissue. 



1. Sections of young umbilical cord and of em- 

 bryos show connective-tissue cells. 



2. Sections of fat and teased fresh pieces of fat. 



3. Salamander skin, dehydrated and mounted with 

 lower side up shows connective-tissue pigment cells. 



