THE COAGULATION OF THE BLOOD. 



TH E causes that lead to the clotting of blood form a 

 subject which seems to possess a peculiar attractive- 

 ness to the investigator of physiological problems. Like 

 the subject of muscular contraction it produces every few 

 years a fresh crop of theories seeking to explain it. But in 

 both cases, the new facts that are discovered often throw 

 fresh difficulties in the way of, instead of shedding new 

 light upon, the vexed question at issue. 



It is, however, useful to pause every now and again, 

 and take stock of the scientific position in matters of this 

 kind. We must start by frankly acknowledging that a 

 final and conclusive theory has yet to be discovered, but a 

 historical retrospect is by no means uninteresting and is 

 often useful. I therefore propose in the following article 

 to sketch briefly the story of blood coagulation in the hands 

 of scientific investigators, and to compare our present 

 knowledge with that of our predecessors. I think it will be 

 acknowledged that we have made some progress of late 

 years, but the progress has consisted rather in discovering 

 our ignorance than in removing it. 



When the microscope first came into use, it was recog- 

 nised that the blood is not a homogeneous red fluid, but 

 consists of a nearly colourless fluid, the plasma, in which 

 are suspended a number of particles which are called the 

 blood corpuscles. Of the two main classes of corpuscles, 

 the red ones are by far the more numerous, and give the 

 red tint to the blood as a whole. The white corpuscles are 

 small and typical animal cells, masses of living material 

 (protoplasm), containing a nucleus. 



In those early days, the clot which occurs in blood after 

 it is shed was supposed to consist merely of a mass of 

 adherent corpuscles. Some held that they stuck together 

 because the blood was no longer in active movement ; 

 others again thought the cooling of the blood after its 

 removal from the body caused the corpuscles to form a 

 coherent jelly, much in the same way that soup sets when 



