372 ANATOMY OF THE RABBIT 



several days, but if the specimen is wanted for use immediately 

 the injection of the coloured mass into the vessels may be made 

 after several minutes, usually with satisfactory results. 



The injection mass may be made by mixing ordinary starch and 

 water to the consistence of thin cream ; then adding a finely-ground 

 colouring material, such as vermilion or a very small quantity of 

 carmine. There is some advantage in using a 5 per cent or even 

 stronger formalin and about one part in seven of glycerin instead 

 of water alone in making up this mass, the arteries having after- 

 wards a brighter appearance, which is doubtless due partly to 

 better preservation and partly to the fixing of the starch in the 

 vessels. The glycerin keeps the starch suspended better. The 

 mass must be thoroughly strained before use, in order to avoid 

 the presence in it of particles which are too large to go through 

 the cannula. The injection is made with a syringe, the latter being 

 provided with a rubber tube of the same kind as that used in the 

 embalming process. The mass is sent in by applying a gentle, 

 even pressure, and it is sometimes advantageous to allow the in- 

 jection to run backward and forward in the tube, each time apply- 

 ing a little more pressure. When the vessels have been filled in this 

 way, the tube is clamped. By drawing on one cord of the ligature 

 the knot is loosened sufficiently to withdraw the cannula, and by 

 keeping a finger pressed on the end of the vessel, the knot may 

 then be drawn tight without loss of injection. 



It sometimes happens, despite ordinary precautions, that the 

 cannula becomes clogged either with settled starch or with coagu- 

 lated blood. In this case it may easily be removed, cleaned, and 

 replaced. The same cannula should always be used. 



During recent years, coloured latex has largely replaced other 

 masses for injection of the blood-vessels in animals to be dissected. 

 It has the advantage of forming a strong, tough, elastic body 

 within each vessel. The material may be obtained from commercial 

 supply houses, which will also provide advice regarding minor 

 precautions that facilitate its use. 



Material prepared according to the directions given above will 

 keep indefinitely, provided, however, that precautions are taken 

 to avoid contamination from the surface. These are especially 

 necessary in view of the thick coating of hairs. It is a good plan, 



