SACHS-ENGELMANN 273 



of protoplasm, which is supposed to bring about the pro- 

 cesses of movement. Sachs attempted, therefore, to com- 

 plete the theory in this direction by introducing a number 

 of further hypotheses, which gave it such a complicated 

 form that there was little hope at the outset of arriving 

 in this direction at a clearer comprehension of the pro- 

 cesses. He bases his view upon four assumptions with 

 regard to the nature of the molecules, or rather molecular 

 complexes, of the protoplasm: (1) That they must possess 

 a definite, but not spherical form ; (2) that they mutually 

 attract one another in proportion to their mass and 

 their distance apart ; (.'3) that each molecule possesses a 

 strong affinity for water, which, however, decreases more 

 rapidly with distance than does the attraction of the mole- 

 cules for one another, so that each molecule is surrounded 

 by a relatively thick envelope of water ; and (4) that the 

 molecules, in addition to their general attraction for one 

 another, also possess so-called directive forces, which depend 

 upon their form, i.e. a sort of polarity, and that these forces 

 tend to bring the molecules into certain definite positions 

 with regard to one another. By the combined effect 

 of all these forces and conditions, a state of unstable 

 equilibrium of the molecules to one another is produced, 

 the consequence of which is that any local disturbance 

 in it immediately spreads throughout the entire mass. He 

 is of opinion in particular that as soon as the distance 

 between two molecules is increased through any circum- 

 stance, their watery envelopes become thickened by attrac- 

 tion of water from the neighbouring " molecular inter- 

 stices," and thus a streaming movement is set up which is 

 continued backwards from the point towards which it is 

 directed. If, now, it is to be admitted, on the ground of 

 the hypothesis put forward, that by an increase in the 

 distance between two molecules their watery envelopes are 

 able to grow, as the result of a diminution in the hindrance 

 which the mutual attraction of the molecules opposes to this 

 growth in thickness of the water envelopes, it is yet in no 

 way intelligible, as far as I am able to judge, why these 

 molecules should then necessarily absorb water from the 



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