62 SMELL, TASTE, ALLIED SENSES 



such as have been described by Jagodowski (1901) in the 

 pike, and the distal ends of these flagella reach through 

 the olfactory mucous to the nasal atmosphere, the odor- 

 ous particles may come directly in contact with them 

 and dissolve in their lipoid substance without pass- 

 ing through an intermediate watery layer. In that case 

 solubUity in lipoid would be the only form of solubility 

 necessary for the introduction of an effective stimulus. 

 That a number of odorous substances are more soluble 

 in lipoid than in water has recently been shown by Kremer 

 (1917) who found that larger quantities of citral, 

 guaiacol, pyridine, and even chloroform and ether would 

 dissolve in a saturated aqueous solution of lecithin than 

 in pure water. Of course the varying capacity for re- 

 action of such materials as may thus become dissolved 

 in the substance of the hairs must profoundly influence 

 stimulation and possibly it is in this direction that the 

 difference between such substances as chlorbenzol and 

 brombenzol is to be explained. But however these de- 

 tails may be worked out eventually, the general opinion 

 that olfactory stimulation is dependent upon some form 

 of solution seems to be beyond question. 



That the material thus dissolved must act chemically 

 on the oLfaotory receptors and not by means of any radia- 

 tion that it may give out seems probable from the fact 

 that olfactory stimuli are substances that are not known 

 to be radio-active. That there is a kind of physiological 

 radio-activity, such as has been claimed recently for po- 

 tassium by Zwaardemaker (1918a, 1920) and as might be 

 urged for the materials of olfactory stimulation, seems 

 extremely improbable from the recent work of R. F. Loeb 

 (1920) and of J. Loeb (1920). Moreover it would be 



