70 THE ELEMENTARY NERVOUS SYSTEM 



before. Soon after this increase of activity was noted 

 over the first chamber, a like increase appeared in the 

 cilia over the third chamber, though the cilia in the inter- 

 mediate region remained motionless. After a time, how- 

 ever, these too began to beat. Kraft concluded, there- 

 fore, that a region of quiescent cilia could transmit im- 

 pulses to increased activity without showing any ciliary 

 movement itself. The subsequent activity of the inter- 

 mediate cilia he believed to be due to mechanical stimula- 

 tion received from the especially excited cilia over the 

 first chamber. It is thus clear, as Engelmann long ago 

 maintained, that ciliated epithelia may transmit impulses 

 to action without any associated mechanical disturbance. 

 These impulses pass through the deeper protoplasmic 

 parts of the tissue and call forth the successive activity of 

 the cilia which thus gives evidence of this transmission 

 wave. Such an activity is sufficiently nerve-like in char- 

 acter to justify the designation neuroid. 



In ciliated epithelia this type of transmission exhibits 

 a feature long ago recognized by Griitzner and especially 

 by Kraft wherein it shows a remarkable resemblance to 

 true nervous transmission in even the more specialized 

 types of central nervous organs. Ciliated transmission 

 is limited as to its spread and direction. If a spot in a 

 relatively quiescent field of ciliated epithelium is mechan- 

 ically stimulated the increased activity of the cilia thus 

 produced does not spread in all directions over the field, 

 but forms a band beginning at the spot stimulated and 

 extending in the direction taken by the transmission wave. 

 This band may become somewhat wider than the spot 

 as one recedes from the region of stimulation, but it never 

 spreads to any considerable extent. This condition justi- 

 fies the conclusion that the individual cells in a ciliated 



