THE BLOOD. 13D 



The blood last drawn is said, from being more watery, to coagulate 

 more quickly than the first. 



The coagulation of the blood is retarded, suspended, or pre- 

 vented by the following means: 



1. Cold retards coagulation; and so long as blood is kept at a tem- 

 perature C. (32 F.), it will not coagulate at all. Freezing the blood, 

 of course, prevents its coagulation; yet it will coagulate, though not 

 firmly, if thawed after being frozen; and it will do so even after it has 

 been frozen for several months. A higher temperature than 49 C. (120 

 F.) retards coagulation by coagulating the albumen of the serum, and 

 a still higher one above 56 C. (133 F.) prevents it altogether. 



2. The addition of water in greater proportions than twice the bulk 

 of the blood, also the addition of syrup, glycerine, and other viscid sub- 

 stances. 



3. Contact with living tissues, and especially with the interior of a 

 living blood-vessel. Blood may be kept fluid in a tortoise's heart after 

 removal from the body for several days, and if the jugular vein of a 

 horse be ligatured in two places so as to include within it blood, and 

 then be removed from the body and placed in a cool place, the contained 

 blood will remain unclotted for hours or even days. 



4. The addition of neutral salts in the proportion of 2 or 3 per cent 

 and upward. When added in large proportion most of these saline sub- 

 stances prevent coagulation altogether. Coagulation, however, ensues 

 on dilution with water. The time during which blood can be thus pre- 

 served in a liquid state and coagulated by the addition of water, is quite 

 indefinite. 



5. In inflammatory states of the system the blood coagulates more 

 slowly although more firmly. 



6. The coagulation of the blood is prevented altogether by the addi- 

 tion of strong acids and caustic alkalies, and also by the addition of a 0.1 

 per cent solution si potassium oxalate, which precipitates the soluble cal- 

 cium salt present in the blood, in the form of insoluble calcium oxalate. 

 Without the presence of soluble calcium salt, blood does not coagulate. 



7. The injection of commercial peptone containing albumoses, or of 

 various digestive ferments, e.g., trypsin or pepsin, into the vessels of 

 an animal appears to prevent or stay coagulation of its blood if it be 

 killed soon after. The secretion of the mouth of the leech, and possibly 

 the blood squeezed out of its body when full, also prevents the clotting 

 if added to blood. 



It is stated that the reason why blood does not coagulate in the living 

 vessels is, that the factors which are necessary for the formation of fibrin 

 are not in the exact state required for its production, and that at any 

 rate the fibrin ferment is not formed or is not free in the living blood, 

 but that it is produced (or set free) at the moment of coagulation by the 



