THE MOVEMENTS AND REACTIONS OF AMOEBA. 21^ 



little above it (Fig. 54). Some, which are at first free, la-ter come in 

 contact. Clearly, Amoeba is able to perform all the activities con- 

 cerned in locomotion without adherence to a solid. The adherence 

 is only necessary that there may be a movement from place to place. 

 The case is quite parallel to that of higher organisms, where contact 

 with the substratum is necessary in order that progression may occur, 

 though all the movements concerned in locomotion may be performed 

 without such contact. 



We are compelled to conclude, therefore, that in the advancing end of 

 an Amoeba or the projecting pseudopodium there is an active move- 

 ment of the protoplasm, of a sort which has not been physically 

 explained. This involves the general conclusion that no physical 

 explanation is at present possible of the locomotion and projection of 

 pseudopodia in Amoeba. 



To account for the contraction of the posterior part of the body, on 

 the other hand, possibly the properties common to Amoeba with other 

 fluids are sufficient. If surface tension may be considered the cause of 

 the contraction of the posterior part of the body, it is notable that it 

 acts as a constant factor, tending always to decrease the surface as much 

 as possible, not as a variable factor. In other words, there is no indi- 

 cation that local increase or decrease in surface tension (see note, p. 

 22^) plays any part in the production of the movements, as is main- 

 tained in the prevailing theories. The part played by surface tension 

 is thus a very subordinate one. 



EXPERIMENTAL IMITATION OF MOVEMENTS DUE TO LOCAL CON- 

 TRACTIONS OF THE ECTOSARC, AND OF THE ROUGHENING OF 

 THE ECTOSARC IN CONTRACTION. 



Besides the sending out of pseudopodia, there are certain other phe- 

 nomena in the movements of Amoeba for which we lack, so far as I am 

 aware, any attempt at a physical explanation. These are the swinging 

 movements, vibrations, and local contractions of pseudopodia, described 

 on pages 177-1 79, and the roughening of the ectosarc in the contraction 

 of pseudopodia or other parts of the body (p. 168). 



These phenomena are in certain details so similar to some that I 

 have observed in inorganic fluids that I believe it worth while to 

 analyze the latter; possibly they give an indication of the direction in 

 which an explanation of the phenomena in Amoeba above mentioned 

 may lie.* 



"In view of the repeated failures of physical explanations in attempting to 

 account for vital phenomena, one does not approach a new attempt of this sort 

 with great confidence. Yet it is desirable that any possibility of this kind should 

 be worked out and submitted to criticism, in order that its truth or lack of truth 

 mav be demonstrated. 



