340 
Smell intensity and electric power do not reach their maximum 
at the same term. For the former it oecurs with butyric acid, for 
the latter with caproic acid. A physiological property cannot, indeed, 
be entirely dependent on merely physical factors. Material volatility 
e.g. may be a matter of necessity for smell; once afloat odorous 
molecules are at the merey of currents of air and diffusion. Further 
on, in the olfactory fissure adsorption to a moist surface is neces- 
sary, but a great number of glands cause the chemical composition 
of the moist layer and consequently also the surface qualities to 
vary from those of water. 
finally the adhesion of the odorous particles to the olfactory 
hairs is certainly a necessary condition, but the influence they exert 
is not determined by the degree of adsorption alone. The mere fact 
that the curves roughly point to such a close relation between the 
electrifying power and olfactory capacity ‘is remarkable. 
A more accurate quantitative measurement of the electric phenom- 
enon may still be obtained by arranging a small dise of just the 
right size at the critical distance of the sprayer and by allowing the 
positive drops to beat against it, while the negative ions rebound 
and disperse. From the time required for a definite deflection, under 
an overpressure of precisely two atmospheres, or from the deflection 
brought about by a definite amount of an odour-solution, say 25 ¢.c., 
the electrifying power may directly be estimated. An inquiry is now 
in progress, but of course it will not enable us to point out a closer 
relation than has already been revealed. 
The other series of substances, inodorous yet evoking an electrical 
charge, has in so far as l was able to ascertain, the property of 
being soluble in water, of lowering its surface-tension, and moreover 
of being sublimable. Whether with these substances (antifebrin, anti- 
pyrin, caffein, etc.) there is any relationship between the electrical 
phenomenon and the intensity of physiological action is a question 
that must be left for further investigation. Many times already 
experimenters have been looking for a relationship between surface- 
forces and physiological or toxic effects among chemically allied 
substances, but their efforts concerned the surface forces acting upon 
lipoid membranes. In the case of odorous substances in an homologous 
series we have to do with the action of surface forces upon a 
capillary layer of water, which no doubt is a much simpler question. 
