268 THE AMERICAN MONTHLY [Sept. 



TJie endotheliurn of the valves may be studied in the 

 same way. To see the arrangement of the connective 

 layers forming the frame work of the latter, proceed 

 thus : Pin a valve to a cork and immerse in picric acid. 

 In 2 hours remove the pins and complete the fixing by 

 leaving it in the liquid for 6 hours. Harden in alcohol, 

 imbed in gum. Cut longitudinal and transverse sections; 

 stain by picro-carmine, examine in acid glycerine. 



ARTERIES. 



. . . .Sections. — After removing the greater portion of 

 the cellular tissue about the aorta, open it lengthwise by 

 scissors. Cut out a little rectangular piece so that its 

 long sides shall be perpendicular to the lumen of the 

 vessel. . . . If we desire sections parallel with the axis of 

 the artery we cut parallel with the small side of the 

 piece ; if perpendicular sections are wanted, section par- 

 allel with the larger side. This apparently puerile sug- 

 gestion is of great importance. . . . The artery should be 

 treated as were the valves. (Fixation by picric acid af- 

 ter extending on cork, hardening in alcohol, imbedding 

 in gum). Sections parallel with the axis are most in- 

 structive. Deeply stain with picro-carmine, wash, 

 mount in water, and allow the following liquid to run 

 under: Glycerine, 50; formic acid, 1; saturated solu- 

 tion of picric acid, 50. 



To dissociate the muscle cells from the middle layer, 

 macerate a piece of aorta for 24 hours in the I alcohol ; 

 with curved scissors remove a bit of the middle coat and 

 spread on a slide with needles. Stain with picro-car- 

 mine, mount in that liquid after partial drying; replace 

 the picro-carmine by a drop of glycerine. 



The elastic plates may be easily demonstrated by dis- 

 sociating a shred of aorta after macerating in a 1 per 

 cent aqueous solution of tartaric acid. 



The endothelium of the internal coat may be shown by 



