loS AN INTRODUCTION TO SCIENCE 



motion. This conclusion being unassailable, they stated the 

 phenomena, which they knew must hold good, as facts. 



William Hewson, "F. R. S. and Teacher of Anatomy," 

 commenced, in 1767, a series of experiments which he 

 published under the title of "An Inquiry into the Properties 

 of the Blood." His methods are admirable, and his con- 

 clusions are drawn with the modesty which should always 

 characterize scientific thought. "Two of the latest writers 

 on this subject agree that if fresh blood be received into a 

 cup, and that cup put into water heated to 98, it will not 

 separate ; nay, they even say that it will not coagulate ; but 

 this, I am persuaded from experiments, is ill-founded."* 

 After reciting experiments which showed that blood kept at 

 the body temperature, as nearly as his apparatus allowed, 

 coagulated even sooner than the same blood left exposed to 

 the temperature of the air, he proceeds to put the matter to 

 a crucial test. He ligatures a vein in the neck of a dog in 

 two places and then covers it with the skin to prevent its 

 cooling. Opening the vein after an interval he found the 

 blood in it coagulated, although coagulation was very con- 

 siderably delayed. In this experiment the blood was kept 

 warm, but it was allowed to come to rest. " Blood, when 

 received into a basin very soon jellies or coagulates. The 

 circumstances in which it now differs from what it was in 

 the veins are these : it is exposed to the air, to cold, and is 

 at rest. The question is, to which of these circumstances 

 its coagulation whilst in the basin is chiefly owing. As the 

 subject seemed to me of importance, I have endeavoured to 

 ascertain the circumstance to which this coagulation is 

 owing by several experiments, in each of which the blood 

 was generally exposed to but one of the suspected causes at 

 a time." He repeats the experiment of ligaturing the vein 

 in two places. "From several experiments made in this 



* " An Experimental Inquiry into the Properties of the Blood," 

 second edition, p. 3, 1772. 



