no AN INTRODUCTION TO SCIENCE 



which all the conditions are artificial. Had Hewson exam- 

 ined the blood only after it was drawn from the body, he 

 would have placed it in contact with a china or metal cup, 

 would have exposed it to air and to dust, would have 

 allowed its halitus or volatile spirit to escape, and in many 

 other respects he would have introduced conditions any one 

 of which he might have mistaken, as they all were mistaken 

 by his successors, as the vera causa of coagulation. 



Whence does the fibrin come ? What is its condition in 

 circulating blood? Prevost and Dumas (1823) studied the 

 chemical properties of fibrin, and decided correctly that it 

 could not be in a condition of solution in circulating blood. 

 It is not a soluble substance. They also observed under the 

 microscope that multitudes of globules, resembling the 

 nuclei of blood- corpuscles, were entangled in the clot, and 

 they inferred that the fibrin was present in the blood as 

 fibrin, but was in some way fixed to, or formed part of, the 

 corpuscles. Their description is not sufficiently clear to 

 enable one to say exactly what was their idea of the relation 

 of the fibrin to the corpuscles. "The attraction which 

 keeps the red matter fixed around the white globules 

 having ceased along with the motion of the fluid, these 

 globules are left at liberty to obey the force which tends to 

 make them combine and form a network, in the meshes or 

 around the plates of which the colouring matter is included 

 along with a great quantity of particles which have escaped 

 this spontaneous decomposition."* Milne-Edwards tells 

 us that "this theory has been adopted by the greater 

 number of the physiologists of the present day."f For his 

 own part, however, he considered that the fibrin "is merely 

 suspended in the mass of the blood in a state of extreme 

 subdivision, and possessed of transparency too perfect to 

 admit of its being seen amidst the surrounding fluid." 



*"Annales deChimie," vol. 23, p. 51. 



f "Cyclopaedia of Anatomy and Physiology," vol. i., p. 43, 1835-6. 



