TRANSFORMING AND REGENERATING OrGAnNs 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 Traité de microbiologic,’ 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 
1Ducnavux, Traité de microbiologie, Vol. II, Paris, 1899. 
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