702 APPENDIX. 



paration is warm enough the injection of size and vermilion is 

 very slowly and carefully forced in, and the progress which is 

 made can be seen by observing the vessels distributed to the 

 respiratory organs. When a sufficient quantity of injection has 

 been introduced, the pipe may be withdrawn, and the hole 

 plugged with a piece of wood cut to the proper size, to prevent 

 the injection again escaping before the size has had time to set. 

 "The vascular system of insects may sometimes be partially 

 injected by forcing the injection into the abdominal cavity, from 

 which it finds entrance into the dorsal vessel, and from thence is 

 distributed to various parts of the body. The injection in the 

 cavity of the abdomen is then allowed to escape. 



"It is very important that the size and vermilion, or other in- 

 jection which is to be thrown into the vessels, should be 

 thoroughly mixed and well strained before being used. The 

 coloring matter, properly powdered, should be placed in a small 

 earthenware mortar, and the melted size or other fluid carefully 

 added by degrees, the whole being constantly stirred until well 

 mixed. When the proper color has been obtained, the whole 

 must be strained through muslin, or through a fine perforated 

 strainer, into another vessel, which should be kept warm. The 

 injection should be well stirred with a wooden stick previous to 

 filling the syringe. 



" We can judge of the intensity of the color by removing a 

 drop of the solution with a stirring-rod, and allowing it to fall on 

 a white plate so as to form a thin stratum, which should have a 

 pretty deep color. It is always better to have too large a quan- 

 tity of the coloring matter rather than too little. 



" Of vermilion, about two ounces will be sufficient for a pint 

 of size ; but it is better in all cases to regulate the quantity by 

 examining the intensity of the color in the manner just men- 

 tioned. 



"When the preparation is warmed through, the injection pro- 

 perly strained, and the pipe fixed in the vessel, we may proceed 

 carefully to inject, taking care that the injection is kept at a pro- 

 per temperature, by allowing it to remain in the warm water- 

 bath during the operation. 



" The air should be first withdrawn from the upper part of the 

 vessel by means of the syringe, after which the stop-cock is 

 turned off and left attached to the pipe. The syringe is then 

 disconnected, and after being washed out once or twice with 

 warm water, is nearly filled with injection, which must be well 

 stirred up immediately before it is taken. The syringe should 

 not be quite filled, in order that the air in the pipe may be made 

 to rise into the syringe through the injection, by the ascent of the 

 piston, before any of the latter is forced into the vessel. The 

 end of the syringe is then to be pressed firmly into the upper 

 part of the stop-cock with a slightly screwing movement. 



" The piston is now very gently forced down by the thumb, 



