536 LECTURE XXIII. 



two experiments lies merely in the fact that when there is a spontaneous 

 coagulation of the blood, the fibrin holds the blood-corpuscles within its 

 meshes and only squeezes out the serum, while by beating the blood the 

 fibrin is separated from the blood-corpuscles. 



The question that interests us first of all is as to the difference between 

 the plasma and the serum. Whereas the normal blood, as it circulates 

 through the blood-vessels, consists essentially of only two constituents, 

 plasma and blood-corpuscles, clotted blood contains three, namely, the 

 blood-corpuscles, serum, and fibrin. In both conditions of the blood we 

 find the corpuscles. They remain unchanged, or at least the red corpuscles 

 do, as far as we know. The plasma, on the other hand, separates into two 

 parts, serum and fibrin. The following scheme represents these relations: 



Blood 



Blood-corpuscles Plasma 



Fibrin Serum 



Blood-clot (when formed 

 spontaneously) 



Blood 



Blood-corpuscles Plasma 

 Serum Fibrin 



Defibrinated blood 



Fibrin is unquestionably formed from the plasma. It was conceivable 

 that it is present as such in the blood under normal conditions, being 

 held in solution while the blood is circulating in the body and only 

 caused to precipitate under definite conditions. On the other hand, it 

 was also believed possible that fibrin is not present as such in the blood, 

 i.e., the plasma, except in the form of a preliminary stage of its development. 

 Careful investigation soon showed the latter view to be the correct one. It 

 is perfectly plain that this peculiar and remarkable phenomenon of the clot- 

 ting of blood which has attracted the attention of many investigators even 

 in remote ages, affords to the animal an important means of protection 

 against undue loss of blood, sufficient in most cases to cause the bleeding 

 to cease. 



The first thorough and systematic investigations, upon which our whole 

 theory of blood coagulation is based, were made by the two scientists 

 Buchanan * and Alexander Schmidt. 2 Each of these men, working inde- 

 pendently, has explained the essential points concerning the clotting of 

 blood. Buchanan made the important observation that hydrocele fluids 



1 Proc. Philosoph. Soc. Glasgow, 2, 1844 (1845). 



a Arch. Anat. Physiol. 1861, 1862; Pfliiger's Arch. 6, 445 (1872); 9, 354 (1874); 11, 

 291 and 515 (1875); 13, 103 (1876). For the literature on the subject, see P. Morawitz: 

 Ergeb. Physiol. 4, 307 (1905). Other comprehensive works on the clotting of blood to 

 which we would call attention are, Alexander Schmidt: Die Lehre von den fermenta- 

 tiven Gerinnungserscheinungen (1876); Zur Blutlehre (1892) and Weitere Beitrage 

 zur Blutlehre (1895); Arthus: Neuere Arbeiten zur Blutgerinnung (1899); E. Schwalbe: 

 Beitrage zur Chemie und Morphologic der Koagulation des Blutes (1900) ; A. Schitten- 

 helm: Zentr. Stoffwechs. u. Verdauungs Krankheiten, 6, 143 (1905). 



