CAUSE OF COAGULATION OF THE BLOOD. 161 



perimentally proven. The experiments cited show conclu- 

 sively that as blood coagulates, out of the body, a vapor is 

 given off which contains some substance capable of preserv- 

 ing the fluidity of the fibrin ; and that ammonia, which is a 

 constituent of this vapor, has this property. But the rigid 

 requirements of our science render it necessary, in order to 

 establish the fact that the evolution of ammonia is the sole 

 and constant cause of coagulation, to show how ammonia is 

 given off under all the varied circumstances under which 

 coagulation of the blood is known to take place. In other 

 words, it must be demonstrated that the evolution of ammo- 

 nia in coagulation is not a coincidence, occurring, it may be, 

 pretty generally, but a necessity. The fact that ammonia 

 added to blood prevents coagulation is not sufficient evidence 

 of this ; for, as we have seen, other substances, such as carbon- 

 ate of soda, have the same effect. 



Are there any circumstances under which coagulation of 

 blood takes place, where ammonia is not, and cannot be, 

 given off? There are observations which seem to answer 

 this question in the affirmative; and it becomes necessary 

 now to carefully study, with reference to this point, all the 

 varied conditions under which the blood will coagulate. 



The view that coagulation of the blood is due to the 

 evolution of ammonia explains perfectly how this process is 

 hastened by exposure to air, by a moderately high tempera- 

 ture, by a vacuum, by the blood flowing slowly in a small 

 stream, and in brief, the various circumstances which modify 

 coagulation out of the body. Its evolution from the blood 

 by the lungs is not incompatible with the fact of the fluidity 

 of the blood in the body, for it is taken up from the tissues 

 as fast as it is eliminated. Some instances, however, of 

 coagulation in the ~body, and some experiments on coagulation 

 out of the body, when, as is thought, ammonia is not and 

 cannot be evolved, seem opposed to the view advanced by 

 Richardson. 



It is easy to understand, adopting the views of Kichard- 

 11 



