vi INJECTION OF BLOOD-VESSELS 99 



which you have already removed the alimentary canal. In the following 

 dissections, use a dissecting lens whenever necessary. 



I. In the heart (Figs. 3, 4, 7, 20 and 21), notice again the ventricle, 

 and the right and left auricles (appearing single in the entire heart), and 

 make out also the conns arteriosus, dividing into two distally, and the 

 sinus venosus (dorsal). 



If the heart is still beating, notice the order of contraction of its 

 different divisions (p. 90). 



Injection Of the Arteries. The tracing of the arteries is greatly 

 facilitated by filling them with some coloured substance. The operation 

 requires, therefore, a coloured fluid or injection-mass capable of 

 traversing the arteries, and some contrivance by which it can be injected 

 into them. 



The most convenient injection-mass is made as follows : 



1. Grind up in a mortar 4 grammes of " French blue" (to be had at 

 the oilman's) with 4 cubic centimetres of glycerine and the same 

 quantity of methylated spirit. 



2. Grind up 50 grammes of common laundry-starch, with 50 cubic 

 centimetres of water and 25 of methylated spirit, and add to the 

 mixture the colour prepared as above. Mix thoroughly and strain 

 through muslin. 



This injection-mass will keep for an indefinite period in a stoppered 

 bottle, requiring only to be stirred up when used. If it is considered 

 too troublesome to make, a simpler but less satisfactory mass may be 

 made by simply stirring up some French blue in water in the proportion 

 of a teaspoonful to a tumbler. 



For injecting the mass into the blood-vessels, the most satisfactory 

 instrument is a brass injecting syringe, holding about one ounce, 

 provided with nozzles of various sizes. This is, however expensive, 

 and an ordinary glass syringe, to be had of any druggist, will answer the 

 purpose very fairly if provided with a proper nozzle or cannula. This 

 latter is made by drawing out one end of a piece of glass tubing about 

 two inches long until it is fine enough to pass into the conus arteriosus : 

 a piece of india-rubber tubing is then used to connect it with the fixed 

 nozzle of the syringe. A still simpler injecting apparatus is furnished 

 by a common ' ' medicine dropper " (see p. 12, and Fig. 25). By alterna- 

 tive squeezing and releasing the cap, fluid is drawn into or expelled 

 from the tube. 



Having provided these ' requisites proceed as f-Sl'lovvs. Open 



H 2 



