Coagulation in drawn blood may be retarded or prevented altogether by a variety of means, of which the following are the most important: (1) By cooling. (2) By the action of neutral salts. (3) By the action of oxalate solutions. (4) By the action of sodium fluoride. Summary.—To summarize then, the following statements may be made: (1) The immediate factor necessary to the clotting of the blood is the fibrin. (2) That blood does not clot normally in the blood vessels before death. (3) That after death blood remains for a long time without clotting, provided some outside agent is not introduced to cause it. Such an agent may be the blood coming in contact with the air, or the blood drainage tube. The one point then to be emphasized is that when a vein is cut, and the blood begins to flow, you know that the blood is not in a coagulated condition. Then work rapidly, put the blood drainage tube quickly into the vein and draw off as much blood as you can before it begins to clot at the end of the tube. The great trouble has been, that the embalmer does not work with precision. He first raises the vein, and exposes it on the surface of the incision. He then raises the artery. He places the drainage tube into the vein, but shuts it off till he is ready with the artery. Now, by the time he has placed the arterial tube in the artery, injected a few bulbs full to see that all is in working order, and has perhaps attended to a few other duties, he is amazed to find that the blood will not flow, that it has clotted. What is the reason? He gave it time to clot after the drainage tube was inserted. A better procedure would be not to touch the vein until every other procedure has been attended to. Then raise the vein, insert the drainage tube and withdraw the blood quickly, and at the same time keep injecting slowly into the arterial system to keep up the needed pressure to keep the blood flowing. (4) That when a clot is once formed in a blood vessel, it is not dissolved by the addition of fluid or any other solution. (5) That sometimes when the blood has become clotted at the end of the drainage tube, it can be loosened up or be slightly pushed away by attaching the pump to the drainage tube and injecting a few bulbs of fluid, which, when it runs out, will again start the flow of blood. CHAPTER V. OSTEOLOGY. =Definition.=—Osteology is the science of the structure and functions of bones. In regard to the treatment of this subject, it is not our aim to take up all the minute details concerning each bone, all we desire is to explain the form, uses and location of some of the principle bones and sets of bones of the body in so far as they may come to be used as landmarks for the embalmer. =The Skeleton.=—The entire skeleton in the adult consists of 200 distinct bones. [Illustration: FIG. 12—The Skeleton.]