INJECTION OF BLOODVESSELS. 621 



as fresli as possible, or after the expiry of sufficient time to allow 

 the rigor-mortis to pass off, the presence of this being very 

 inimical to the success of the injection. The part should be 

 thoroughly warmed, by soaking in warm water for a time pro- 

 portionate to its bulk; and the injection, the syringe, and the 

 pipes should also have been subjected to a temperature sufficiently 

 high to insure the free flow of the liquid. The force used in 

 pressing down the piston should be very moderate at first ; but 

 should be gradually increased as the vessels become filled ; and 

 it is better to keep up a steady pressure for some time, than to 

 attempt to distend them by a more powerful pressure, which 

 will be certain to cause extravasation. This pressure should be 

 maintained 1 until the injection begins to flow from the large 

 veins, and the tissue is thoroughly reddened ; and if one syringe- 

 ful of injection after another be required for this purpose, the 

 return of the injection should be prevented by stopping the 

 nozzle of the jet-pipe when the syringe is removed for refilling. 

 When the injection has been completed, any openings by which 

 it can escape should be secured, and the preparation should then 

 be placed for some hours in cold water, for the sake of causing 

 the size to " set." 2 



434. Although no injections look so well by reflected light, 

 as those which are made with vermilion, yet other coloring sub- 

 stances may be advantageously employed for particular purposes. 

 Thus the yellow chromate of lead, which is precipitated when a 

 solution of acetate of lead is mixed with a solution of chromate 

 of potass, is an extremely fine powder, which " runs" with great 

 facility in an injection, and has the advantage of being very 

 cheaply prepared. The best method of obtaining it, is to dis- 

 solve 200 grains of acetate of lead and 105 grains of chromate 

 of potass in separate quantities of water, to mix these, and then, 

 after the subsidence of the precipitate, to pour off the super- 

 natant fluid, so as to get rid of the acetate of potash which it 

 contains, since this is apt to corrode the walls of the vessels, if the 

 preparation be kept moist. The solutions should be mixed cold, 

 and the precipitate should not be allowed to dry before being in- 

 corporated with the size, four ounces of which will be the pro- 

 portion appropriate to the quantity of the coloring-substance pro- 

 duced by the above process. The same materials may be used 

 in such a manner that the decomposition takes places within the 

 vessels themselves, one of the solutions being thrown in first, 

 and then the other ; and this process involves so little trouble or 

 expense, that it may be considered the best for those who are 



1 A simple mechanical arrangement for this purpose, by which the fatigue of main- 

 taining this pressure with his hand is saved to the operator, is described in the " Micro- 

 graphic Dictionary," p. 354. 



2 The kidney of a sheep or pig is a very advantageous organ for the learner to practise 

 on ; and he should first master the filling of the vessels from the arterial trunk alone, 

 and then, when he has succeeded in this, he should fill the tubuli urinifrri with white 

 injection, before sending colored injection into the renal artery. The entire systemic 

 circulation of small animals, as mice, rats, frogs, &c., may be injected from the aorta ; 

 and the pulmonary vessels from the pulmonary artery. 



