INJECTED PREPARATIONS '. OPAQUE INJECTIONS. 741 



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 proportionate to its bulk ; and the Injec- 

 tion, the Syringe, and the pipes should also have been subjected to 

 a temperature sufficiently high to ensure 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* 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 re-filling. 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.'t 



578. For Opaque Injections, the best colouring-matter, when 

 only one set of vessels is to be injected, is Chinese Vermilion. 

 This, however, as commonly sold, contains numerous particles of 

 far too large a size ; and it is necessary first to reduce it to a 

 greater fineness by continued trituration in a mortar (an agate or 

 a steel mortar is the best) with a small quantity of water, and then 

 to get-rid of the larger particles by a process of ' levigation,' 

 exactly corresponding to that by which the particles of coarse sand, 

 &c, are separated from the Diatomacea? (§ 237). The fine powder 

 thus obtained, ought not, when examined under a magnifying 

 power of 200 diameters, to exhibit particles of any appreciable 

 dimensions. The Size or Gelatine should be of a fine and pure 

 quality, and should be of sufficient strength to form a tolerably 

 firm jelly when cold, whilst quite limpid when warm. It should 

 be strained, whilst hot, through a piece of new flannel ; and great 

 care should be taken to preserve it free from dust, which may best 

 be done by putting it into clean jars, and covering its surface with 

 a thin layer of alcohol. The proportion of levigated Vermilion to 

 be mixed with it for injection, is about 2 oz. to a pint ; and this 

 is to be stirred in the melted Size, until the two are thoroughly 



* A simple mechanical arrangement for this purpose, by which the 

 fatigue of maintaining this pressure with his hand is saved to the operator, 

 is described in the " Micrographic Dictionary," 2nd Edit., p. 383. 



t 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 uriniferi with white injection, before sending 

 coloured injection into the renal artery. The enth;e Systemic Circulation 

 of small animals, as Mice, Rats, Frogs, &c, may be injected from the 

 Aorta, ; and the Pulmonary vessels from the Pulmonary Artery. 



