294 THE MICROSCOPE AND ITS REVELATIONS. 



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/ 1 



688. For opaque injections, the best coloring-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 tritu- 

 ration 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, etc., are separated from the Diatomacece ( 300). The fine 

 powder thus obtained, ought not, when examined under a magnifying 

 power of 200 diameters, to exhibit particles of any appreciable dimen- 

 sions. The size or gelatine should be of a fine and pure quality, and 

 should be of sufficient strength to form a tolerable 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 pre- 

 serve it free from dust, which may be best done by putting it into clean 

 jars, and covering its surface with a thin layer of alcohol. The propor- 

 tion 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 incorporated, after which the mixture should be strained 

 through muslin. Although no injections look so well by reflected light 

 as those which are made with vermilion, yet other coloring substances 

 may be advantageously employed for particular purposes. Thus a bright 

 yelloiv is given by the yellow chromate of lead, which is precipitated when 

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

 tass; this 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 dissolve 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-oif the supernatant 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 incorpo- 

 rated with the size, four ounces of which will be the proportion appro- 

 riate to the quantity of the coloring-substance produced by the above 

 process. The same materials may be used in such a manner that the de- 

 composition takes-place 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 novices in the operation, and who are desirous of perfecting 

 themselves in the practice of the easier methods, before attempting the 

 more costly. By M. Doyere, who first devised this method, it was sim- 

 ply recommended to throw-in saturated solutions of the two salts, one 



1 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 arte- 

 rial trunk alone, and then, when he has succeeded in this, he should fill the tu- 

 buli uriniferi with white injection, before sending colored injection into the renal 

 artery. The entire systemic circulation of small animals, as Mice, Rats, Frogs, 

 etc., may be injected from the aorta; and the pulmony vessels from the pulmo- 

 nary artery. 



