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alkali to acid «iibstaiices, under the formation of fibril-flakes, and, 

 under favoui-able circumstances, coagulation of the colloid fibril. 

 Perhaps we have to deal here with a fact, the importance of which 

 to physiology and pathology goes far beyond the problem of blood- 

 coagulation, I do not however, wish to enter into this question in 

 this paper ; 1 shall restrict myself to emphasize the possible signifi- 

 cance of this fact, as a foundation for the solution of the problem 

 concerning the nature of blood-coagidation. 



It has been demonstrated that the transition of fibrin from the 

 sol-state into the gel-state may be brought about by the following 

 factors : 



a. by acids in weak concentration, or by neutralization ; 



h. by acid salts, also at an acid reaction of the medium ; 



c. by acids in strong concentration ; 



d. by saturated salt-solutions ; 



e. by calcium-chloride solutions. 



This formation of flakes in flbrinogen-solutions is only a special 

 case of a quality, characteristic of colloids and albumens in general, 

 at least as regards the factors mentioned sub a, c, and d. The 

 colloid fibrin, however, is distinguished from other albumens, except 

 casein, in being able to agglutinate in fibres under favourable cir- 

 cumstances, to form an elastic gel, a real coagulum such as is 

 formed when blood coagulates. 



Will our knowledge of the relation between fibrinogen and fibrin 

 on the one hand, and of the factors which cause fibrin to pass from 

 the sol-state into the gel-state, on the other, enable us to give a 

 satisfactory explanation of the phenomenon of natural blood-coagulation? 



This would indeed seem to be the case if only it could be demon- 

 strated that in blood, substances are found or can be formed, whose 

 action would be identical with that of one or more of the factors 

 mentioned above. 



For this purpose it might be investigated if acid salts are formed 

 in the blood, or a hypothesis might be formed as to the importance 

 of CO2 in this respect, after the manner of some other investigators. 



All this seems superfluous, however. Keeping in view the data to 

 be found in the literature on the problem of blood-coagulation, it 

 stands to reason that we should think in the first place of the 

 nudeoprotekls and of calcium. The nucleoproteids, substances derived 

 from decomposed nucleated cells, possess as we know properties 

 of an acid, wiiile more especially Pekelharing and his school have 

 established beyond doubt that these substances can effect blood- 

 coagulation. 



