272 PROTOPLASM 



possessed by the particles within the protoplasmic body 

 were to increase constantly in a certain direction, the water 

 would necessarily be set in movement in this direction, 

 since it would be attracted by the particles with the greater 

 power of imbibition ; thus a streaming movement would 

 be brought about, with which an increase in the volume 

 of the particles with stronger powers of imbibition would at 

 the same time be connected. In 1867 he put the latter 

 point more in the foreground, without, however, basing the 

 actual explanation of the streamings on it, which was given 

 in just the same way as in 1865. In 1867 Hofmeister 

 more specially declares that, as a result of the increase or 

 decrease in the thickness of the envelope of water round 

 each molecule of protoplasm endued with different powers of 

 imbibition, changes of place must be produced in the mole- 

 cules, and their middle points brought closer together or 

 carried farther apart. Although he now remarks that this 

 conception of the alteration in the position of the molecules, 

 as the result of different degrees of imbibition, is completely 

 sufficient for the " demonstration " (" Versinnlichung ") of the 

 " mechanics of protoplasm," yet, in the further course of his 

 description, he gives exactly the same explanation of the 

 currents again which he had already put forward in 1865, 

 where he speaks, indeed, of the above-mentioned water 

 currents, but does not try to refer the streaming movements 

 to alterations of this kind in the position of the molecules. 



Hofmeister, when he thought that the mechanics of 

 protoplasm could be interpreted by the idea that the watery 

 envelopes of the molecules possess a variable thickness, had 

 yet overlooked one important point, namely, the observed 

 fact that a muscle cell when it contracts becomes thickened 

 in correspondence with its shortening, which his hypothesis 

 in the form put forward by him was not able to explain. 



Sachs also (1865) came forward as an opponent of the 

 contraction theory in the case of vegetable protoplasmic 

 movements. He regards Hofmeister's theory as admissible 

 in general, but in need of still further elaboration in order 

 to lead to a clearer understanding, since it did not explain 

 the actual causes of the varying imbibition of the particles 



