THE FROG 93 



Corn starch 400 parts. 



2 per cent, chloral hydrate 400 parts. 



95 per cent, alcohol 100 parts. 



Coloring substance and glycerin (equal parts) 100 parts. 



Unless the starch is quite free from lumps it should be 

 ground in a mortar. The coloring substances most com- 

 monly used for the arteries are chrome yellow (lead chro- 

 mate), vermilion (murcuric sulphid), and red lead. In 

 order to inject the smaller arteries successfully it is neces- 

 sary that the color should be finely powdered and free from 

 lumps; it is often advisable to grind it thoroughly in a mor- 

 tar. An extremely fine chrome yellow may be made by dis- 

 solving 100 grams lead acetate and 45.5 grams potassium 

 bichromate each in a liter of water. After complete solu- 

 tion, mix and allow the precipitate to settle. Pour off the 

 supernatant fluid, and wash the precipitate in several waters 

 to remove the potassium acetate. The reaction gives about 

 100 grams chrome yellow, which should not be allowed to 

 dry before using. 



The constituents of the starch mass should be thoroughly 

 mixed by stirring, and the mass strained through muslin, 

 with frequent stirring. The starch and color quickly settle, 

 hence the mixture must be stirred before using, and occa- 

 sionaly while it is being used. It will keep indefinitely. 



For injection select the largest frogs, to be used only for 

 the study of the arterial system ; they should be killed with 

 ether. Open up the body cavity in the manner directed 

 in the text for the study of the viscera, and cut away 

 all that part of the pectoral girdle between the fore-limbs, 

 taking care not to leave any sharp projecting points of bone 

 which might injure the arteries. Cut away the pericardium 

 so as to expose the heart completely. 



