AUGUST 19, 1921 ALSBERG : PHYSIOLOGICAL CHEMISTRY 323 



"anaesthetic" groups, "narcotic" groups, "tetanic" groups, and the 

 like. 



Our present-day conception of protoplasm is dififerent. We no 

 longer think of a giant living molecule so unstable that its decomposi- 

 tion and. continuous reconstruction constitute the phenomena of life. 

 We no longer consider protoplasm as homogeneous. We believe it to 

 be heterogeneous, to consist of a series of phases, an emulsion, a series 

 of fine droplets and particles in suspension.^ According to the laws of 

 surfaces, which I shall have to ask you to take for granted tonight, 

 as we have no time to consider them now, some substances will con- 

 centrate at surfaces and this concentration will be greater the greater 

 the curvature of the surface.^ Therefore, in such a system as an 

 emulsion you have membranes formed automatically at all surfaces, 

 and so it seems to be with protoplasm. You must conceive of these as 

 chemical membranes, as mere surface layers, not necessarily visible 

 under the microscope, representing the very great concentration at the 

 surface of a droplet of one or more of the substances dissolved in the 

 droplet or in the surrounding medium. Each droplet is then a sort 

 of test tube shut off to a certain degree from the other droplets and from 

 the liquid in which it is suspended. Phenomena can therefore go on 

 in such a droplet without affecting the other droplets except indirectly. 

 Such a conception of protoplasm very greatly simplifies, as we shall 

 see later, our conception of the physiological action of chemical sub- 

 stances since instead of being a purely chemical concept it is physical 

 as well as chemical. It leaves room for such considerations as the 

 surface effect of the substance, its solubility in the membrane, in the 

 droplet, in the various phases of a gel, etc., etc. 



With the old conception of protoplasm as a homogeneous chemical 

 entity the physiological action of a substance was referred merely to 

 its chemical character and reactivity. This point of view impeded 

 rather than aided progress. With the acceptance of the idea of proto- 

 plasm as a physical system, rather than as a chemical structure, the 

 conviction has gained ground that the physiological action of a sub- 

 stance depends not rnerely upon its chemical structure but also upon 

 its physical properties, or rather those properties" that lie on the frontier 

 between physics and chemistry, such properties as solubility, diffusi- 



= C. L. Alsberg. Mechanisms of cell activity. Science N. S. 34: 97-105. July 28, 

 1911. 



* W. M. Bayliss. An introduction to general physiology. (Longmans, Green & Co., 

 I^ndon, 1919.) Chap. I. 



' G. GiEMSA. Neuere Ergebnisse der Chemotherapie. Archiv Pharm. 257: 194. 1919, 



