PHYSIOLOGICAL CHEMISTRY 335 



in the action of the calcium salts and in the part played by the 

 enzyme.) 



Conditions which retard Clotting. ( 1 ) Cold receive the blood into 

 a vessel placed in ice (i.e. keep it at a temperature a little above 

 freezing point). The enzyme action is inhibited by cold. The blood 

 clots on warming. 



(2) Contact with blood-vessel wall. "The living test tube." This is 

 made by ligaturing in two places a vein of a large animal, such as the 

 jugular vein of the horse. In the tube thus formed the blood does not 

 clot, and if it be hung up the corpuscles gradually sink to the bottom, 

 leaving the unclotted plasma above. 



(3) Addition of certain neutral salts. "Salted plasma" (cf. Experi- 

 ment II.). 



(4) Addition of a soluble oxalate. "Oxalate plasma" (cf. Experi- 

 ment III.) 



(5) Addition of a soluble citrate. " Citrate plasma " (see Experi- 

 ment V.). 



(6) Addition of a soluble fluoi'ide. "Fluoride plasma." This plasma 

 will not clot upon the addition of calcium (see Experiment V.). 



(7) Addition of leech extract (Hirudin). This is a secretion produced 

 by the salivary glands of the leech, and which can be obtained by 

 extracting the heads with water. It acts because it contains an anti- 

 thrombin. 



(8) Contact with oil. Receive the blood into a smooth vessel smeared 

 with oil. 



(9) Intra-vitam methods. These consist in injecting certain substances 

 into the blood-vessels of the animal before bleeding it. These sub- 

 stances are : 



(a) Commercial peptone, which consists mainly of proteoses. 



(/?) Soap solution. 



(y) A weak alkaline solution of nucleo-protein injected slowly the 

 so-called " negative phase " of nucleo-protein injection. 



Peptone acts by causing the liver to form a large amount of anti- 

 thrombin, which normally keeps blood from clotting inside the vessels. 

 The exact action of nucleo-protein is not well understood. 



Conditions which hasten Clotting. (1) Body temperature. 



(2) The addition of some clotted blood (clot or serum). 



(3) Agitation, e.g. whipping the blood with a bunch of twigs. This 

 is a very general method of keeping blood fluid when it is not desired 

 to study the phenomena of clotting. 1 



*It is important to remember that this is no longer normal blood, but de- 

 fibrinated blood. 



