V] OF THE PROTOPLASMIC COLLOIDS 443 



what to reconsider our position, and to enquire whether the true 

 surface-tension of a Hquid film is actually responsible for all that 

 we have ascribed to it, or whether certain of the phenomena which 

 we have assigned to that cause may not in part be due to the 

 contractility of definite and elastic membranes. But to investigate 

 this question, in particular cases, is rather for the physiologist: and 

 the morphologist may go his way, paying little heed to what is no 

 great difficulty. For in surface-tension we have the production of 

 a film with the properties of an elastic membrane, and with the 

 special peculiarity that contraction continues with the same energy 

 however far the process may have already gone ; while the ordinary 

 elastic membrane contracts to a certain extent, and contracts no 

 more. But within wide limits the essential phenomena are the 

 same in both cases. Our fundamental equations apply to both 

 cases alike. And accordingly, so long as our purpose is morpho- 

 logical, so long as what we seek to explain is regularity and definite- 

 ness of form, it matters little if we should happen, here or there, 

 to confuse surface-tension with elasticity, the contractile forces 

 manifested at a liquid surface with those which come into play at 

 the complex internal surfaces of an elastic solid. 



