INJECTION BY VEINS. 387 



but when joined with tallow two parts, they correct each other, as the 

 one is too thin, and the other rather too thick. Butter or hog's lard 

 make of themselves pretty good injection. 



Watery Injections. — Glue dissolved in water alone makes a good 

 minute injection. Before you dissolve it by heating it, steep it in 

 water twelve hours ; then heat it gently till the whole is dissolved ; after- 

 wards strain it and drop some of it on any cold substance, and you will 

 know its consistence. When it is somewhat thicker than common jelly, 

 it is of a proper consistence. ' Size ' is better than * glue ' for white 

 injection, being clearer. Isinglass, prepared in the same manner with 

 the preceding, makes an injection similar to it. All fine injections 

 require more colour than coarse ones ; for, as it is to run into much 

 smaller vessels, it often becomes more and more transparent, and there- 

 fore requires such a quantity of colour as to render it opake when it is 

 most minutely diffused, either in very small vessels, or on any surface. 



A watery or spirituous injection is best for injecting thin parts that 

 are to be dried and rendered transparent ; viz. all sorts of membranes, 

 and such parts as seem to be membranous when dry, as the stomach, 

 intestines, &e. 



Preparing parts to be injected for Veins. — We can only inject the 

 large trunks of veins in the extremities ; for when we put a pipe into a 

 vein and throw in our injection, it in general only passes in a straight 

 line from that to the heart, for at the entrance of other veins into this 

 vein there are generally placed valves which keep the injection in a 

 straight line to the heart ; and if these valves are not sometimes exactly 

 at the mouths of collateral veins, yet you will generally find they are 

 within an inch of it, so that you have only so much injected. However, 

 on the foot and back of the hand the veins in general form an arch on 

 both sides, and we have all the veins arising from this arch injected ; 

 but still this would not inject all the large veins if there were not 

 other communications between the veins of different parts ; but we find 

 that a vein on one side shall send a canal of communication to a vein 

 of the other side, which canal having no valves, the injection passes 

 freely, and injects the veins of the other side. 



Warm water should be injected into veins before injection, for two 

 reasons ; first, to warm the parts ; and secondly (and indeed the most 

 material), to wash out the blood, especially if the injection is of a white 

 colour ; and great care should be taken that ail the water is squeezed 

 out before you throw in your injection, or any air that may be in the 

 veins ; for these often make interruptions in the larger trunks. One 

 would imagine that the air, water, or blood would be carried along the 

 veins before the injection, and would be let out at the great trunk of 



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