SUGGESTIONS TO TEACHERS. 461 



oils, as xylol, benzol, and the like. These should be added 

 gradually as their necessity and uses become apparent. 



Injection Masses. For the study of the veins and arteries 

 and other tubular structures it is often desirable to inject into 

 them foreign substances which prevent their collapse and ren- 

 der them easy of identification. For this purpose a syringe 

 and some rubber tubing and small canulas are necessary. In- 

 jection masses to be satisfactory should be fluid when injected 

 and be able to " set " or harden, after injection. For ordinary 

 work the following will serve : 



1. Starch injection mass: 



Dry laundry starch i volume. 



2 l / 2 per cent, aqueous solution chloral hydrate . . i volume. 



95 per cent, alcohol ^4 volume. 



Coloring mixture j4 volume. 



The coloring mixture is prepared by mixing equal parts of 

 95 per cent, alcohol, glycerine, and dry carmine (vermilion, 

 chrome yellow or Prussian blue). The solid color should be 

 ground into small portions of the fluids in a mortar so that no 

 lumps will be present in the mass. This mixture does not spoil 

 with age, but must always be well stirred before using and 

 the injecting must be rapidly done, as the solids settle quickly. 



2. Gum or Gelatine Injection Masses. It is often desirable 

 to have a mass which can be forced through the finer vessels, 

 as the blood capillaries, so that the arteries and veins may 

 both be filled by one injection into an artery near the heart. 

 The following solution if injected warm will pass the capil- 

 laries. If the gelatine solution is first injected and then fol- 

 lowed by a starch mass of a different color, the veins will 

 ultimately contain the former and the arteries the latter, as 

 the starch will not pass the capillaries, and thus both may be 

 easily studied because of the contrast in color. 



Gelatine solution (i part gelatine to 6 or 8 of 



water) i volume. 



Glycerine carmine ' - 1 A volume. 



Chloral hydrate (concentrated solution) .......... 



2 per cent., by weight, of the entire mass. 



