166 THE BLOOD. 



ganism, ammonia, a substance capable of maintaining the 

 fluidity of the fibrin, is given off from coagulating blood. 

 "We may suppose that ammonia separates itself from one 

 portion of the blood, and is retained in another. An experi- 

 ment by Eichardson gives color to this supposition, for in 

 one experiment on the passage of blood- vapor through blood, 

 he found that the lower part coagulated while the upper part 

 remained fluid; and on examination, ascertained, in expla- 

 nation of this, that the tube which carried the vapor into the 

 blood did not extend to the bottom of the vessel. 1 



The effect of foreign bodies on coagulation is not more 

 inexplicable than the operation of inert substances in certain 

 chemical processes ; as the action of the oxide of manganese 

 in the formation of oxygen from the chlorate of potash ; or, 

 to take a process more like the one under consideration, the 

 formation of crystals on threads and projections in vessels, or 

 the escape of electricity from points. Examples of this kind 

 in the organic world are numerous, and we are content to 

 say that these facts are entirely beyond explanation, in the 

 present state of our knowledge. We should hardly be sur- 

 prised, then, at our inability to explain the tendency which 

 the presence of foreign bodies has to induce the deposition of 

 so coagulable a substance as fibrin. The theory that coagu- 

 lation of the blood is always, or even generally, due to the 

 contact of foreign substances, or tissues which have lost their 

 vital properties and act as foreign substances, must be rejected 

 as opposed to experiment and observation. When, as hap- 

 pens in the interior of the body, the blood coagulates under 

 circumstances when the process will not admit of direct 

 experimentation as far as the evolution of volatile substances 

 is concerned, the best we can do is to apply, as far as possible, 

 the facts which are proven with regard to coagulation out of 

 the body, when the phenomena can be minutely studied. 

 Here, at least in the human subject and in mammals, it 

 seems demonstrated to be due to the evolution of ammonia. 



1 Op. tit., p. 269. 



