388 PRACTICAL ANATOMY. 



the vein or at the heart, if it was a whole body ; but practice shows us 

 the contrary, and it is easily to be accounted for ; viz. the small vein 

 that you put your pipe into is not only to inject the vein leading from 

 that in a straight line, but to inject many collateral ones. Now, if 

 there be any air, water, or blood in any of the collateral veins, that air, 

 tfcc. will be carried on towards the large trunk before the injection ; but 

 the injection will by this time have got into the large trunk beyond the 

 mouth of this collateral vein, by means of the vein that led immediately 

 from the pipe. This air, &c, then, being thrown into the large trunk, 

 where there is injection both before and behind, it must make an inter- 

 ruption at that part; but the interruption will not rest here if you 

 continue to throw in your injection, for it will be carried forwards by 

 the succeeding injection, and it will at the same time forward the column 

 of injection that is before it. 



Now that we have explained the cause of one interruption, we can 

 easily see how many may be formed, as there are more than one collateral 

 vein. One would remedy this by throwing in the injection till all 

 those collateral veins have communicated with the common trunk, and 

 letting the injection run out at the other end, till the last interruption 

 had come out at the end of the vein, and then tie up the end to keep 

 the succeeding in ; but we cannot always throw in so much injection 

 by such a small pipe as one would in such cases ; however, we always 

 leave the end of the great vein open till we see the injection come out 

 by it. 



When the veins of a leg or arm are injected, they should not be 

 handled or compressed while the injection is fluid in them, but should 

 be hung up by their ends that are next the body. This will prevent 

 the injection from getting out of the smaller veins into the large ones, 

 because the valves will not allow it to return again, and of course will 

 become empty. 



The gravid uterus should be injected by both veins and arteries at one 

 and the same time, so as to have them run nearly equal where the 

 placenta adheres. 



Of Corroded Preparations. 



The whole affair of injecting for corrosion, or making corroded pre- 

 parations, requires more attention than any one other method of making 

 anatomical preparations. They are always intended for the common 

 distribution of the larger vessels, and therefore in parts that cannot be 

 dissected with any degree of perfection or accuracy. As the animal 

 parts are to be destroyed, and only the injection saved, the injection is 

 only to be considered as a cast, and the vessels the mould ; therefore 



