708 TRANSACTIONS OF SECTION I. 



remain barren, never contributing towards physiological achievement. To what 

 extent its adoption may be an intellectual solace is a question which does not 

 fall within the scope of physiology. Certain physiological phenomena are 

 especially brought forward as necessitating the assumption of vitalistic or biotie 

 conceptions ; among these are the phenomena of nervous activities, the formation 

 and activities of enzymes, and the passage of substances through living membranes. 

 The question of the nervous activities will be dealt with later; but as regards the 

 diffusion of gases or substances in solution through cellular membranes a few 

 general considerations may be advanced now.^ The passage of substances into and 

 through non-living membranes is modified in regard to both the velocity and the 

 selective character of the passage by a large number of factors, among which are 

 nature of substance, pressure, osmotic index, temperature, and the structural, 

 electrolytic, and chemical characters of the membrane. Tissue membranes, whether 

 animal or vegetable, possess a complicated particulate structure, and it is obvious 

 that experiments must be carried out extensively on dead tissue membranes in 

 order to determine how far the general particulate arrangement may modify the 

 rate and character of the passage. In this respect our present information is not 

 sufficiently extensive to warrant any definite general statement, and such experi- 

 mental evidence as exists opens up difficult problems in molecular physics which 

 still await solution ; moreover, the presence of electrolytes, by assisting adsorption, 

 appears to modify the apparent rate and character of the total passage, and further 

 experiments are necessary on this point. But in the living membrane, especially 

 when it is composed of cellular units, the whole question is additionally com- 

 plicated by the great probability that the cells are the seat of chemical processes 

 the nature of which is imperfectly known ; such processes constitute the meta- 

 bolism of the cells, It would, therefore, be somewhat surprising if the phenomena 

 of the passage of substances through such cellular membranes were in strict 

 accord with the passage of similar substances through non-living membranes 

 which have not the same particulate framework and are not the possible seat 

 of similar chemical processes. The statement, therefore, that any discrepancy 

 between the two classes of phenomena necessitates the assumption of a peculiar 

 vital directive force disregards the circumstance that between the conditions in 

 the one case and those in the other lies a large and little explored field ; moreover, 

 such a statement implies, without any warrant, that any physico-chemical ex- 

 planation must necessarily be insufficient in the case of the living membrane, 

 although it is realised that there may be active chemical processes of whose opera- 

 tions we have at present little exact knowledge. 



What possible justification is there, therefore, for branding as hopeless all 

 further physical and chemical investigation of certain aspects of the phenomena by 

 attributing these to vital directive forces ? The gaps and imperfections of the 

 palfeontological record were triumphantly vaunted by the opponents of evolution ; 

 and now that the work of successive years has convincingly contributed towards 

 the filling up of these gaps not only has this objection collapsed, but the hypothesis 

 of special creations which it supported has been involved in its fall. There are 

 indications that the discrepancies in diff'usion phenomena throu^^h widely different 

 structures may be knit by the results of experiment on intermediate modifications. 

 It may be many years before these are completed, but the introduction of vitalism 

 or biotie energy as a fictitious causative explanation is so opposed to the spirit and 

 the progress of science that we may safely predict the complete abandonment of 

 this position at a comparatively early date. 



I venture now to define my own position in regard to this matter. I assert 

 that, although the complexity of living tissues makes our present knowledge 



' The conception of Ostwald as to the action of catalytic substances is extremely 

 suggestive in connexion with the activities of enzymes, both intracellular and extra- 

 cellular. It is possible that the changes brought about by enzymes may, with the 

 growth of our knowledge in physical chemistry, be shown to be of the same order as 

 those which slowly occur in the absence of enzymes, and that the enzyme itself by 

 iacilitating adsorption phenomena may merely act by accelerating the velocity of 

 the special change. See Leathes, ProUems in Animal Metabolism (London : Murray, 

 1906). 



