88 PHYSIOLOGICAL CHEMISTRY. 



iation coagulates more slowly than arterial blood. The coagulation 

 may be retarded or prevented by the addition of acids, alkalies, or 

 ammonia, even in small quantities ; by concentrated solutions of 

 neutral salts or alkalies and alkaline earths ; also by egg-albumin, 

 solutions of sugar or gum, glycerin, or much water; also by receiv- 

 ing the blood in oil. The coagulation may be prevented by the in- 

 jection of an albumose solution or by an infusion of the leech into 

 the circulating blood, but this infusion of the leech acts in the 

 same way on blood just expelled. The coagulation may be facil- 

 itated by raising the temperature; by contact with foreign bodies, 

 to which the blood adheres ; by stirring or beating it ; by admission 

 of air; by diluting with very small amounts of water; by the ad- 

 dition of platinum-black or finely-powdered carbon ; by the addition 

 of lac-colored blood, which does not act by the presence of dissolved 

 blood-coloring matters, but by the stromata of the blood-corpuscles 

 (WooLDRiDGE, Nucif), and also by the addition of the leucocytes 

 from the lymphatic glands, or a watery saline extract of the lymph- 

 atic glands, testicles, or thymus. The active constituent of such a 

 watery extract is, according to WOOLDRIDGE, an albuminous body 

 containing lecithin, which he calls tissue fibrinog en. 



An important question to answer is why the blood remains 

 fluid in the circulation while it quickly coagulates when it leaves 

 the circulation. 



When the blood leaves the vein it comes under new, abnormal 

 conditions. It cools off, it comes in contact with the air, its 

 motion stops, and it is deprived of the influence of the living 

 walls of the vessels. That the cooling is not the reason of the 

 coagulation is proved by the fact that cooling is a good means of 

 retarding coagulation. That the contact with air is not essential 

 is shown by the fact that when blood is collected over mercury, so 

 that it cannot absorb or expel any gas, it likewise coagulates. 

 That the cessation of the motion does not cause the coagulation 

 follows, since blood collected over mercury coagulates whether it is 

 shaken or not, and further from the fact that motion, such as 

 beating the blood, facilitates the coagulation. 



The reason why blood coagulates on leaving the body is there- 

 fore to be sought for in the influence which the walls of the living 



