LABORATORY SUGGESTIONS 537 



Beside the materials mentioned above it is often desirable to have other sub- 

 stances, — as sugar, acids, salts, and some of the oils, as xyolol, benzol, and t^e 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 render them easy of identification. For this purpose a syringe 

 and some rubber tubing and small canulas are necessary. Injection 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. 



2j^ per cent, aqueous solution chloral hydrate i volume. 



95 per cent, alcohol !^ volume. 



Coloring mixture 34 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 wiU 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 capillaries. If the gelatine solution 

 -is first injected and then followed 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 }i volume. 



Chloral hydrate (concentrated solution) 



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



The gelatine should be soaked in cold water and then slightly heated until 

 dissolved. The glycerine carmine may be prepared as follows: thoroughly pul- 

 verize and mix 3 grams of carmine with a little water, with enough ammonia added 

 to dissolve the carmine. Add 50 grams of glycerine. Mix and filter. Add 

 gradually to this mixture enough acidulated glycerine (glycerine and acetic acid 

 in the ratio of 10 to l) to give a slight acid reaction to the carmine glycerine mass. 



5. Materials for Study. — The types of animals needed for this course, with the 

 exception of the marine representatives, may be secured in almost any locality, 

 if sought at the proper time. The teacher should become entirely familiar with the 

 common animals to be found within a reasonable distance from his school. It 

 is especially necessary to know the life most abundant in the various ponds, lakes 

 and streams. A close watch should be kept on the material gathered from each 

 place, and a record kept of the various localities in which each useful type has 



