Physiology of Central Nervous System 67 



same time offered a different conception of reflexes. The flight 

 of the moth into the flame is a typical reflex process. The 

 light stimulates the peripheral sense-organs, the stimulus passes 

 to the central nervous system, and from there to the muscles of 

 the wings, and the moth is caused to fly into the flame. This 

 reflex process agrees in every point ^vith the heliotropic effects 

 of light on plant organs. Since plants possess no nerves and no 

 ganglia, this identity of animal with plant heliotropism can 

 force but one inference — these heliotropic effects must depend 

 upon conditions which are common to both animals and plants. 

 At the end of my book on heUotropism^ I expressed this view 

 in the following words: ''We have seen that, in the case of 

 animals which possess nerves, the movements of orientation 

 toward light are governed by exactly the same external condi- 

 tions, and depend in the same way upon the external form of the 

 body, as in the case of plants which possess no nerves. These 

 heliotropic phenomena, consequently, cannot depend upon 

 specific qualities of the central nervous system." On the other 

 hand, the objection has been raised that destruction of the 

 ganglion-cells interrupts the reflex process. This argument, 

 however, is not sound, for the nervous reflex arc in higher animals 

 forms the only protoplasmic bridge between the sensory organs 

 of the surface of the body and the muscles. If we destroy 

 the ganglion-cells or the central nervous system, we interrupt 

 the continuity of the protoplasmic conduction between the 

 surface of the body and the muscles, and a reflex is no longer 

 possible. Since the axis cylinders of the nerves and the 

 ganglion-cells are nothing more than protoplasmic formations, 

 we are justified in seeking in them only general protoplasmic 

 qualities, unless we find that the phenomena cannot be explained 

 by means of the latter alone. 



2. A further objection has been raised, that although these 



1 Loeb, J., Der Heliotropismus der Tiere und seine Uebereinstimmung mit dem 

 Heliotropismus der Pflanzen, Wurzburg, 1890. A preliminary note on these 

 experiments appeared January, 1888. 



