— 109 — 



Further, there are a number of substances which are very volatile, 

 and which according to their chemical structure belong to the odorous 

 substances, and yet do not smell. For such cases a plausible explanation 

 may perhaps also offer itself. The air charged with the substance 

 in question, when inhaled, comes in contact with the olfactory cells. 

 The latter possess in their hair -like attachments a considerable en- 

 largement of their free surface, and an extended contact takes place 

 therefore between the air and the substance of the olfactory hairs. 

 There will once more occur an interchange of the dissolved constitu- 

 ents between contiguous solvents. The quantitative conditions are 

 again governed by a coefficient of dissolution. If the latter is un- 

 favourable towards a transition into the substance of the olfactory 

 hairs, then the molecules, even when they for themselves have a strong 

 odour, will produce no excitement. 



Finally we will mention two experiments x ) : intermission of the 

 olfactory excitement by means of periodical interruption during */ 4 of 

 a second of the current of air, I. inside the nose, and 2. outside, 

 in the olfactometer. The two experiments have opposite results. In 

 the former case, when the interruption takes place in the nasal cavity, 

 the sensation is intermittent; in the latter, when the interruption is 

 effected in the olfactometer, it is continuous. Zwaardemaker there- 

 fore concludes that the solution of the odorous molecules in the sub- 

 stance of the olfactory hairs takes place instantaneously, and that the 

 fusion of the olfactory excitement does not originate in the terminal 

 apparatus of the sense organ as such, but on the contrary in the air 

 passages leading to it. 



Phyto-physiological Notes. 



Experiments made by E. Charabot and A. Hebert 2 ) with regard 

 to the acid-content of plants, show that the leaf, i. e. the organ of 

 assimilation in which the hydrocarbons are worked up, is richest in 

 free volatile acids. The content of volatile acids differs for each indi- 

 vidual organ; the same applies to the individual stages of development. 

 For example, it diminishes particularly when the inflorescence is in 

 course of development; it increases during the unfolding of the blossoms, 

 and finally again decreases. In the case of the geranium and the sweet 

 basil plants, and also in the green organs of the sweet and bitter orange 

 trees, the conditions are wholly identical. In the orange blossoms, 

 however, the content of volatile acid is larger than in the stalk. Plants 

 grown in the dark carry a greater proportion of acid in the roots than 

 in the leaf. The suppression of efflorescence effects an increase of the 

 acid-content in the leaf, to the disadvantage of the other organs. 



*) Archiv fur Anatomie und Physiologie 1904, 43. 

 2 ) Compt. rend. 138 (1904), 17 14. 



