10 BULLETIN OF THE UNIVERSITY OF WISCONSIN. 



to chemical action upon them. Now in order to get into con- 

 tact with the end-organs a substance must be in solution. This, 

 however, is not of itself sufficient. To get into the taste-bulb, 

 the mouth of which is always covered with mucous, and to get 

 at the nerve, the dissolved substance must diffuse with a fair 

 •degree of readiness; and finally, when it has come into contact 

 with the nerve terminus, it must be capable of acting chemi- 

 cally on the protoplasm of the same, thus causing the irritation 

 that is interpreted as taste. Many substances are tasteless sim- 

 ply because they are insoluble; others, although sufficiently sol- 

 uble, do not diffuse readily enough to come into contact with 

 the nerve terminus; and still others, which though soluble and 

 sufficiently diffusible, are devoid of taste because they fail to 

 react chemically with the protoplasm of the nerve. 



It is evident that for each substance there is a certain mini- 

 mum amount that must be present in order to cause sufficient 

 irritation at the nerve. This amount will naturally be relatively 

 less in the case of those substances that react more intenselv 

 with the protoplasm of the nerve terminus. Again, in the case 

 of those substances that because of very slow diffusion possess 

 but little taste, the solutions must be relatively much stronger 

 in order that sufficient substance may come into contact with 

 the nerve, for the speed of diffusion of a substance is propor- 

 tional to the difference in concentration that exists between the 

 two layers in contact. No doubt the mechanical action of rub- 

 bing the tongue against the palate as we do in tasting aids in 

 brino-ina- the substance to be tasted into contact with the taste- 

 organs. We should, other things being equal, expect a sub- 

 stance that diffuses readily to exert an effect on the end-organs 

 in less concentrated solution than a substance that diffuses more 

 slowly. The electrical conductivity of solutions of electro- 

 lytes is dependent upon the number of ions present and the 

 speed with which they move through the solution. From this 

 it is clear that the conductivity of electrolytes and their speed 

 of free diffusion are closely connected, and we should conse- 



