Physical Properties of Protoplasm 157 



A large number of indicators have been injected into the interior 

 of proteus with the idea of determining a possible relation between an 

 excess of H+ or OH~ ions and the extraordinary water-holding-power 

 of the endoplasm. Azolitmin, sodium alizarin sulphonate, tropeolin 

 ooo No. i, methyl orange and congo red, dissolved in from J to f 

 molar cane sugar have been so far employed. A neutral to slightly 

 alkaline reaction is shown by all the indicators. It seems probable 

 then that the concomitant variation in water-holding-power of dif- 

 ferent regions of the cytoplasm is the mechanism by which Ameba 

 proteus moves and is associated with an excess of OH~ ions. 



A number of operations were performed on the ectoplasm of 

 Ameba proteus for the purpose of determining the relation between 

 movement and surface tension changes. The results of shallow and 

 deep cuts in the ectoplasm have already been given. The outer 5 to 7 

 microns of the pseudopods were cut away in some animals, and in 

 others small doses of distilled water were injected into the ectoplasm. 

 The removal of the outer end of a pseudopod was usually followed by 

 rapid closure of the incision. The injection of distilled water into 

 the ectoplasm had no noticeable effect on the formation of pseudopods. 

 By means of such operations the rigid ectoplasm was either removed, 

 for a short time, from a given area of the surface or at least greatly 

 weakened; yet, no tendency to the formation of pseudopods was 

 ever observed, in such weakened surface areas. These facts seem to 

 justify the conclusion that surface-tension changes play a negligible 

 role in the movement of Ameba proteus. Furthermore, it may be 

 recalled, that the outer surface of Ameba proteus is a semi-rigid solid 

 of from 5 to 12 or more microns in thickness, and it has still to be 

 shown, that the changes, in the tension of the surface film, that are 

 commonly assumed to occur, can appreciably affect the underlying 

 semi-rigid ectoplasm. 



The nutrient solution in which the amebae were grown was slightly 

 alkaline in reaction. 



Proteus usually recovers from the large doses of neutral salts 

 and sugar in much less than an hour, almost certainly by throwing 

 them off. 



