104 DYNAMICS OF LIVING MATTER 



nervous system consists only in causing a contraction of muscular or 



FIG. 18. The secretion of mucus on the skin of Amblystoma under the influence of a constant 

 current. The animals were kept in a trough of water through which a current passed. The 

 current lines were straight and parallel with the longitudinal axis of the animal. The black 

 dots indicate the spots where the secretion of mucus appeared. The drawing shows that the 

 glands secrete at the anode side of the animal where the current lines cut its surface. 



contractile elements which result in the contents of the mucous glands 

 being squeezed out. The secretion is partly, however, a direct effect of 

 the current on the skin, and results finally in the 

 disintegration of the latter. In this case we may be 

 dealing with an electrolytic effect due to secondary 

 chemical reactions. Budgett and I found that these 

 anodic effects of the current on Infusorians and 

 Amblystoma can be imitated by applying NaHO 

 to these organisms. Whatever the cause of the 

 secretion may be, we are not justified in identifying 

 the disintegration of an Infusorian or the skin of 

 an Amblystoma with the tetanus of a muscle. 



It is not our intention to give more than the 

 general idea of irritability and stimulation. Besides 

 chemical and electrical stimulation, mechanical stimu- 

 lation plays an important role. When a nerve has 

 been put into a decalcifying solution for some time, 

 or has lost water, it becomes extremely sensitive to 

 slight mechanical agitation. When a nerve reaches 

 the climax of its sensitiveness, it suffices to knock on the table that 



FIG. 19. The same 

 experiment as in 

 Fig. 18 carried out 

 with pieces of 

 Amblystoma. 



