LESSON XVIII. 



THE LYMPHATIC SYSTEM. 



1. Epithelioid cells of serous membranes. 



Behead a pithed frog, squeeze the body upwards 

 to remove as much blood as possible. Fasten out the 

 lower coil of the intestine with the mesentery (cp. 

 Lesson xvn. 9); wash it with '75 p.c. sodium 

 sulphate ; add a drop or two of *2 p.c. silver nitrate, 

 in 5 minutes wash with sodium sulphate. Cut away 

 the intestine, expose the mesentery to light in distilled 

 water. When the outlines of the surface cells show 

 (about hour), place the mesentery on a slide, drain 

 off the water, stretch, drop on it 95 p.c. alcohol to fix 

 it, place in alcohol for 5 or more minutes. Mount in 

 balsam. 



Note the epithelioid cells covering the mesentery. 

 They are large and flat ; and for the most part poly- 

 hedral. 



2. Epithelioid cells of lymphatic 1 spaces. 



Follow the directions given in Lesson xv. 9, up 



1 The dissection is simpler in the male frog, cp. Footnote p. 137. 



