2. Syringe.—This is usually made to contain about two ounces. On each side of the part next to the handle is a ring, so that the finger may be thrust through it, and the thumb may work the piston as in an ordinary syringe. The plug of the piston must be “packed” with wash-leather, and fit so closely as to be perfectly air-tight; and if, when it has been used awhile, it is found that some of the liquid escapes past the plug into the back part of the body, it must be repacked, which operation will be best understood by examining the part. These syringes are made of various sizes, but in ordinary operations the above will be all that is needed. The nozzle is about an inch long, and polished so accurately that there is no escape when the pipes are tightly placed upon it dry.

3. The pipes are usually about an inch long, to the end of which are affixed thicker tubes so as to fit the nozzle, as before mentioned, whilst a short arm projects from each side of these, so that the silk or thread which is used to tie this artery, &c., upon the thin pipe may be carried round these arms, and all danger of slipping off prevented. The pipes are made of different sizes, from that which will admit only a very fine needle (and this will need now and then to be cleaned, or to be freed from any chance obstruction), to that which will take a large pin. These sizes must always be at hand, as the vessels of some subjects are exceedingly minute.

4. Stopcock.—This is a short pipe like a small straight tap, which fits accurately upon the end of the syringe like the pipes, and also takes the pipes in the same manner. The use of this is absolutely necessary when the object is so large that one syringe full of liquid will not fill it. If no preventive were used, some part of the liquid would return whilst the syringe was being replenished, but the stopcock is then turned as in an ordinary tap, and all danger of this effectually removed.

5. Curved needles.—These are easily made by heating common needles at the end where the eye is situated, and bending them with a small pair of “pliers” into a segment of a circle half an inch in diameter. They are, perhaps, more convenient when the bent part is thrown slightly back where it commences. The pointed end is then thrust into a common penholder, and the needle needs no re-tempering, as the work for which it is wanted is simply to convey the thread or silk under any artery or vessel where it would be impossible to reach with the unassisted fingers.

6. A kind of forceps, commonly know by the name of “bullnose forceps,” will be constantly required during the process of injecting. These are short, usually very strong, but not heavy, and close very tightly by their own spring, which may be easily overcome and so released by the pressure of the fingers. When any vessel has not been tied by the operator, and he finds the injected fluid escaping, one of these “bulldogs” may be taken up and closed upon the opening. This will cause very little interruption, and the stoppage will be almost as effectual as if it were tied.

7. When the ordinary mode of injection is employed, it is necessary that the preparations be kept warm during the time they are used, otherwise the gelatine or size which they contain becomes stiff, and will not allow of being worked by the syringe. For this purpose we must procure small earthenware or tin pots of the size required, which will differ according to the kind of work to be done; and to each of these a loose lid should be adapted to protect it from dust, &c. These pots must be allowed to stand in a tin bath of water, under which a lamp or gas flame may be placed to keep the temperature sufficiently high to insure the perfect fluidity of the mixture. The tin bath is, perhaps, most convenient when made like a small shallow cistern; but some close it on the top to place the pots upon it, and alter the shape to their own convenience.

8. We will now inquire into some of the materials which are needed in this operation; the first of which is size. This substance is often used in the form of glue, but it must be of the very best and most transparent kind. To make the liquid which is to receive the colours for the usual mode of injecting, take of this glue seven ounces, and pour upon it one quart of clean water; allow this to stand a few hours, and then boil gently until it is thoroughly dissolved, stirring with a wooden or glass rod during the process. Take all impurities from the surface, and strain through flannel or other fine medium. The weather affects this a little as to its stiffness when cold, but this must be counteracted by adding a little more glue if found too liquid.

9. Instead of glue, gelatine is generally used, especially when the work to be accomplished is of the finer kind. The proportions are very different in this case, one ounce of gelatine to about fourteen ounces of water being sufficient. This, like glue, must be soaked a few hours in a small part of the cold water, the remainder being boiled and added, when it must be stirred until dissolved. A good size may be made by boiling clean strips of parchment for awhile, and then straining the liquid whilst hot through flannel; but when the injections are to be transparent, it is of the greatest importance that the size be as colourless as possible. For this purpose good gelatine must be employed, as Nelson’s or Cox’s: some persons of experience prefer the latter.

10. Colours.—The size-solution above mentioned will need some colouring matter to render it visible when injected into the vessels of any animal, and different colours are used when two or more kinds of vessels are so treated, in order that each “set” may be easily distinguished by sight. The proportion in which these colours are added to the size-solution may be given as follows:—

11. For—