The skin about the needle hole is then gently washed with a fifty-per-cent solution of hydrogen peroxid, dried with a sterile cotton sponge and the opening sealed with a drop of collodion. Subsequent treatment of the parts will be considered later.
14. Solidification of Paraffin in Needle.—This occurs only when paraffins of high melting points are employed in liquid form in the syringe, and is due to the rapid cooling of the paraffin in the small metallic cannulæ, or needle, wherein it sets more readily, since the volume contained therein is very small, often not more than two or three drops.
This cooling establishes a pluglike formation in the distal end of the needle, which prevents a proper use of the syringe, often breakage, and when suddenly liberated by an extra pressure on the piston rod causes a rapid discharge of the contents of the syringe to an extent not desired with the result of hyperinjection.
This fault was one of the most annoying in the early days of such injections when syringes of ordinary pattern, such as the Pravaz, or those built like the ordinary hypodermic, were used. It was not unusual to have the paraffin cool in the needle so quickly between the latter in the flame of an alcohol lamp that the syringe became unmanageable and broke in the hands of the operator. Since that time new and more useful syringes have been introduced by various operators which overcome this difficulty, yet with them, too, come the employment of semisolid paraffins or mixtures thereof. Yet, as some authors insist upon using paraffins of high melting points, it may be well to rehearse their methods of overcoming this annoying intraneedle solidification.
Eckstein surrounds the syringe and needle shaft, except the tip of the needle, with a rubber tubing, as shown in [Fig. 284], to act as an insulator, and thus, for a time at least, keep the preparation liquid. Before filling the syringe he heats it by several immersions in and internal washings of hot sterile water. To prevent the paraffin from setting in the exposed tip of the needle he draws into the filled syringe a few drops of hot water, which are injected into the tissues, causing no objection to the method.
Fig. 284.—Eckstein Method of Insulating Needle and Syringe.
Paget and Harmon Smith warm the needle in hot sterilized or even boiling water. Previous to this Smith cools the contents of the syringe drawn into it at a temperature of 120° F. by immersing the latter in a bath of sterilized water at a temperature of 80° F.
From the above it will be noted that Smith advocates using the injections in semisolid state being ejected in a thin, cylindrical thread. A syringe of special construction, as referred to later, is, of course, required for such work.
Quinlan has invented a so-called paraffin heater, as shown in [Fig. 285], in which the paraffin is kept in solution by the syringe being surrounded by a continuous flow of hot water. A plain and very objectionable syringe is shown in the illustration, and while the preparation in the syringe is thus kept in a liquid state the solidification in the needle is not overcome.