THE LIVING SUBSTANCE. 125 



Living organisms are surrounded as masses by a general 

 external pellicle of protoplasmic membrane, within and continu- 

 ous with which, is a complex web of delicate, irritable, contrac- 

 tile, membranes. The mass pellicle, whether it define the 

 limit of one or of innumerable cells, expresses the contact sur- 

 face of the organism as such in its relation with environment. 

 For it, environment is of a twofold nature, being compounded 

 of an internal and an external set of contact conditions. 



The external set of conditions is, to great degree, beyond 

 control of the substance, except indirectly through aid of its 

 internal environment which bears a constant relation in both 

 kind and arrangement to the needs of the physiological powers 

 of the substance, and seems to be controlled by it in a twofold 

 way. 



The internal web of protoplasm, on the other hand, is physi- 

 cally surrounded by, and in contact with, an environment upon 

 which it acts and to which it reacts in a multiplicity of ways. 

 This is more or less completely within its control, yet influ- 

 ences it largely and even to some extent controls it ; physically 

 and chemically. Being met here by the undying question of 

 priority of control, it is possible to say only, that, granting a 

 possibly complete, final control of the substance by physical 

 and chemical conditions, yet in the existing state of things 

 visible to us as structure, the substance is seen acting through 

 and upon an existing internal environment. In this way the 

 certain conditions necessary for its renewal are detected, pur- 

 sued and chosen by the organism. These the living substance 

 as such, acting still through existing internal conditions, pro- 

 ceeds to transmute and to arrange with reference to its own 

 general and local needs. 



[118] The internal environment of the living substance is 

 finally, as has been shown, inseparable for us from lamellar 

 subdivisions of the interalveolar foam. Even supposing we 

 could isolate and retain in a living condition for this purpose 

 considerable quantities of the continuous substance of Biit- 

 schli's structure, it would be impossible by the most minute 

 chemical analysis to determine more of even constant results — 

 such as proteids — than that they were either necessary constitu- 



