TRANSFORMING AND REGENERATING ORGANS 635 



how the nature of the contact could possibly influence these 

 processes, and I do not think that anyone else has thus far 

 offered an explanation. While studying the literature on the 

 coagulation of the blood I came across Duclaux's account of 

 this process in his Trait6 de microbiologie, 1 and it seemed 

 to me that if his notions are correct they might also 

 be applied to our problem of contact-heteromorphosis. 

 According to Duclaux it is the character of the contact 

 applied to the leucocytes which decides whether the enzyme 

 of coagulation, the plasmase, becomes effective or not. As 

 long as the leucocyte touches the endothelium of the blood- 

 vessels the blood remains liquid because the contact of the 

 leucocytes with the endothelial cells does not allow the fibrin 

 enzyme to act. If, however, the leucocyte touches a piece of 

 glass the plasmase becomes active and causes coagulation. 

 If the glass is covered with a layer of oil coagulation does 

 not occur. Duclaux assumes that surface tension phenomena 

 decide the setting free of plasmase on the part of the leuco- 

 cyte. Whether this latter assumption be correct or not mat- 

 ters little for our purpose. We only need to carry the 

 analogy between the influence of contact upon the state of 

 matter of fibrinogen and the state of matter of certain col- 

 loids in the Hydroids far enough to assume that both depend 

 upon definite enzymes becoming active through certain forms 

 of contact acting upon the cells in which they are formed. 

 In the case of the blood a solidifying enzyme, in the case of 

 the polyps a liquefying enzyme is made active if the leuco- 

 cyte or the polyp come in contact with glass or some other 

 solid body. 



These considerations possibly allow of a wider application 

 than to the mere case of contact-heteromorphosis. When a 

 piece of our skin is cut off, the cells of the margin of the 

 wound begin to multiply and spread out over the gap. We 



1 DUCLAUX, TraiM de microbiologie, Vol. II, Paris, 1899. 



