STRUCTURE AND PROPERTIES OF PROTOPLASM 73 



prevented from drying up by a little water in the chamber. The earliest 

 and best form was Engelmann's (figured by Verworn, 520). A simpler 

 form was introduced by Pfeffer (" Physiology," 3, 338); it can be bought 

 from various dealers, who also supply, especially for bacteriological purposes, 



Fig. 12. — Electric slide, adapted from common materials; X-J-. 

 View of upper surface and vertical section. 



still simpler forms. An efficient gas-stage can be adapted from strips of 

 window-glass, glass tubing, and glue, with a coating of collodion to protect 

 the latter from moisture; the construction is sufficiently illustrated by the 

 accompanying figure (Fig. 13). 



In the study of the above relations the student must guard 

 against preconceived expectations, and keep his mind open 

 for results as they are, even when 

 these are negative. In one of these 

 relations, the electrotonic, we are 

 dealing with a kind which never 

 occurs naturally. The observed 

 response, therefore, cannot be ex- Fig. 13.— Gas-chamber, adapt- 



1 • J U„ • „-C „J„„4-„ ED FROM GLASS PLATES AND 



plained upon any basis 01 adapta- 



TUBES J X^. 



tion, but must have another meaning. View of upper surfac6| with boMom 



Correlated With these relations is ° r interior dotted, and vertical 



i section. 



the effect produced upon protoplas- 

 mic activity by the presence of more or less (down to practi- 

 cally no) water, with the very important ecological consequences; 

 and on this subject the student should seek information in the 

 literature. 



We now resume our consideration of the different ways in 



