98 HOW TO WORK 



The student may inject with this mixture, and then try the Prussian 

 blue fluid recommended in p. 93, and compare the results. 



185. Mercurial Injections are not much used for microscopical 

 purposes, although mercury was much employed formerly for injecting 

 lymphatic vessels and the ducts of glandular organs. The pressure 

 of a column of mercury a few inches in height is alone sufficient to 

 force some into the vessels. The mercurial injecting apparatus 

 consists of a glass tube, about half an inch in diameter and twelve 

 inches in length, to one end of which has been fitted a steel screw 

 to which a steel injecting pipe may be attached. The pipes and 

 stopcocks must be made of steel, for otherwise they would be de- 

 stroyed by the action of the mercury. 



Of Injecting the Vessels of the Higher Animals. 



186. Of the Practical Operation of Injecting. It is generally 

 stated that a successful injection cannot be made until the muscular 

 rigidity which comes on shortly after death, and which affects the 

 muscular fibres of the arteries as well as those of the muscles them- 

 selves, has passed off; but I have found that most perfect injections 

 may be made before the muscles begin to contract, that is, within a 

 few minutes after the death of the animal. All my fine injections 

 have been made less than five minutes after death. 



The student will find that the process of injecting will be learnt 

 after a few trials, and although he may quite fail in the first attempts 

 he makes, I earnestly recommend him not to give up, for this mode of 

 investigation is of the greatest advantage, and by it we learn facts of 

 great anatomical importance. Every one engaged in the investiga- 

 tion of the anatomy of tissues in health and disease, should be able 

 to inject well, and by employing the fluids recommended, it will be 

 found that injections can be made without much sacrifice of time. 



The steps of the process of transparent injection are very similar 

 to those taken in making the opaque injections, except that when 

 size is employed, the specimen must be placed in warm water until 

 wann through, otherwise the size will solidify in the smaller vessels 

 and the further flow of the injecting fluid will be prevented. Soaking 

 for many hours is sometimes necessary for warming a large prepara- 

 tion through, and it is desirable to change the warm water frequently. 

 The size must also be kept warm, strained immediately before use, 

 and well stirred up each time the syringe is filled. 



In the first place the following instruments must be conveniently 

 arranged : 



The syringe thoroughly clean and in working order, with pipes, 



