Scientific Proceedings (39 ). 



gether with suitable controls, were then sealed with paraffin and 

 incubated at 36° C. In testing for liquefaction, each gelatin 

 culture and also the control tube were diluted with an equal 

 amount of distilled water and filtered through paper. A visco- 

 simeter tube was selected of sufficient caliber so that the control 

 diluted gelatin passed through in about four minutes. With this 

 control time as a basis, the degree of change Induced in the gelatin 

 by the cultures under consideration could be readily and accurately 

 determined. 



no (520) 



On the nature of chemical stimulation and on the influence of 

 neutral sodium salts on various forms of chemical 

 stimulation. 



By RALPH S. LILLIE. 



[From the University of Pennsylvania.] 



Evidence from many sides indicates that the primary change 

 in the stimulation of an irritable tissue is a sudden increase in the 

 permeability of the boundary layers or "plasma-membranes" of 

 the constituent cells or elements The resistance to the escape 

 of diffusible substances, including carbon dioxide, is thus dimin- 

 ished, and there results a corresponding acceleration of the energy- 

 yielding oxidations. With increase in the permeability to ions, 

 there is naturally also associated a change in the electrical polariza- 

 tion of the plasma-membrane — hence the characteristic "action- 

 current" of stimulation. The primary and critical change, in- 

 crease of surface permeability, may be produced by the electric 

 current, by sudden changes of temperature or contact, by mechani- 

 cal shock, or by the action of various chemical substances. 



Chemical stimulation, on this view, results from the action 

 of those substances which affect the constituents of the plasma- 

 membrane in such a manner as suddenly to increase its permea- 

 bility to the critical degree required. Now the plasma-membrane 

 is primarily a colloidal structure, consisting mainly of prothins 

 and lipoids intimately intermixed, possibly intercombined. We 

 should, therefore, expect its structure or consistency to be altered, 

 and its permeability correspondingly increased or decreased, by sub- 



