COAGULATION OF THE BLOOD 107 



great detail by Aristotle because he believed that the process 

 of coagulation resembled the setting of a solution of gelatin, 

 was subsequently added the explanation that the blood is 

 kept from coagulating as long as it is in a state of motion, 

 but clots when it comes to rest. What explanation could be 

 more natural ? The soldier was found on the battlefield 

 lying in a pool of blood which had come to rest, grown 

 cold, and coagulated. The clotting was due to cold and 

 rest. 



This was the accepted explanation until the middle of the 

 last century. Indeed, it held its own until much later, not- 

 withstanding Hewson's demonstration of its insufficiency. 

 In jnedical writings of the eighteenth century we constantly 

 meet with the statements that "Blood coagulates when ex- 

 posed to a moderate degree of cold." " Blood coagulates 

 when it is deprived of the attrition to which it is exposed 

 when circulating within the vessels of the body." Such neg- 

 ative statements are unexceptionable. But we also meet 

 with positive assertions which certainly were not based upon 

 experience. "The blood will not coagulate if the cup into 

 which it is received be kept at the temperature of the body." 

 "If the blood be kept in motion by rapid stirring with a 

 glass rod it is hindered from setting a clot." It would seem 

 to us, with our modern axiom " Check your references," to 

 have been easy to put such assertions to the test : especially 

 easy in the days when the traditions of his profession directed 

 a surgeon to let blood in almost every case he attended, as 

 an obviously remedial measure which he might safely adopt 

 before he proceeded to inquire as to what was amiss with 

 the patient. But these statements were not based upon ob- 

 servation. They illustrate a very different method which was 

 more commonly pursued by the medical writers of that time. 

 Accepting the authority of Aristotle and his successors as 

 unquestionable, they argued that if blood coagulates when it 

 leaves the body, because it grows cold and comes to rest, it 

 follows that it will not coagulate if it is kept warm and in 



