THE LIVING SUBSTANCE. 2 1 



substance ? And finally, which part of the constant results is 

 constant as living substance ; which but as its environment ? 



A still more radical question has not yet been disposed of : 

 how are we to know that there is in the whole compound 

 anything more than interaction, under physical controls, born 

 of their physical arrangement ; of non-living, of chemical 

 materials ? 



All of these questions, not excluding the last, have received 

 for me illumination from study of the inclusions of living proto- 

 plasm ; and yet more light from study of the continuous sub- 

 stance. Though not answered, they receive limitation which 

 may later help us to an answer. 



Nothing is more common in protoplasm than an areal organi- 

 zation, more or less unstable, of the vital phenomena, so that 

 such areas are traversed by the same special phenomena, and 

 the whole may be called physiologically homogeneous through- 

 out. Yet in such area of organized physiological function, the 

 inclusions of Biitschli may or may not show homogeneity in 

 kind or size, but may be thoroughly heterogeneous.^ 



While this is possibly explicable by supposing homogene- 

 ousness in character of the finer froth inclusions, this is but to 

 emphasize the answer already indicated ; and further, to show 

 that not only must we not look to the inclusions of BUtschli's 

 structure for the basis of such homogeneity of function ; but 

 that we shall find it in the interalveolar stuff. 



A sensitively organized activity, and reaction to stimuli, 

 throughout an area whose inclusions are mingled solids and 

 fluids, and of all sizes, may hardly be interpreted as physical 

 interaction between a homogeneous lamellar substance and such 

 chemical and physical heterogeneity. Neither diffusion nor 

 surface tension can readily be brought into play here. On the 

 other hand, the continuous substance in such areas, as in all 

 others where organized physiological activities are found, has 

 definite and most homogeneous characters. 



[17] In the section on contractility it will be shown that in 

 this most important activity, so far as all optical evidence goes, 

 the alveolar contents form the passive group of elements, 



1 See Striation — fibrillar. 



