130 ELEMENTARY PHYSIOLOGY. [XII. 



flows out, when the bleeding has ceased take 

 a small glass caunula having a piece of india- 

 rubber tubing over one end and filled with 

 normal salt solution and insert it into the aortic 

 bulb, tie it near or at the branching of the 

 aortae with a silk thread. Then take a syringe 

 full of normal salt solution, and the tubing being 

 also full of salt solution gently force the nozzle 

 of the syringe into the tubing, being careful 

 that no air-bubbles get in at the same time. 

 Then slowly inject the salt solution : this should 

 be repeated until the fluid issuing from the 

 venous sinus is perfectly clear ; sop up the fluid 

 and inject with water, then inject once or twice 

 a '2 p. c. solution of nitrate of silver, sopping up 

 the fluid which issues from the sinus; inject 

 water to wash out the nitrate of silver, place the 

 frog in a basin of water and cut out the intes- 

 tine ; cut through the mesentery at its junction 

 with the intestine and lay open the intestine, 

 brush away its epithelial coat and expose it to 

 light in water or in 30 p. c. alcohol. The out- 

 lines of numerous vessels will soon be visible ; 

 then cut out a piece, spread it out on a slide 

 with the inner surface uppermost, wash with 

 alcohol of increasing strength, clear and mount 

 in Canada balsam 1 . 



1 If the tissue be left too long before it is mounted the cells as 

 well as the cement substance will become black. From the frog 

 injected as above a piece of the mesentery, or of the lungs, or of the 

 bladder, may be mounted. 



