LOCOMOTORY DIRECTIVE MOVEMENTS 547 



or solutions depends on like or unlike alterations in the protoplasm. When we 

 remember that aerotactic organisms often exhibit no chemotactic sensitivity, 

 and that fern antherozoids are not aerotactic, we must obviously regard aero- 

 taxis and chemotaxis as perfectly distinct sensitivities. Similarly, organisms 

 which are sensitive, for instance, to potassium salts are not necessarily sensi- 

 tive to oxygen. In short, it is probable that we must assume that there are 

 as many types of chemotaxis as there are chemical substances, or groups of 

 substances, distinguished by the organism. Rothert (1901), in fact, has shown, 

 in the case of a species of Amylobacter, that chemotaxis in relation to two 

 different substances may indicate a difference in sensitivity in the organism, for 

 he found that this species was chemotactically sensitive both to ether and to 

 meat extract. If both types of taxis are dependent on the same sensitivity, 

 according to Weber's Law, the liminal intensity of the stimulus for unilateral 

 action of meat extract will be raised by a homogeneous solution of ether. That 

 is not the case, however. Further investigations on this subject will lead us, no 

 doubt, to extremely important and interesting results as to the powers possessed 

 by organisms for distinguishing between different chemicals and the limits of 

 these. [Shibata (1905 b) has, with the aid of this method, been successful in 

 showing that it is possible to decrease the sensitivity of the antherozoids of 

 Isoetes to malic acid by using homogeneous solutions of fumaric acid. The 

 effects produced by these two substances on the perceptive apparatus are the 

 same, in other words, the antherozoids could not distinguish between these two 

 substances. On the other hand, the sensitivity of the antherozoids to salts of 

 the potassium group, e.g. of potassium, rubidium, &c., is quite different (Buller, 

 1900 ; Shibata, 1905 b).] 



What is the exact nature of the first effect of the chemotactically active 

 body and on what the chemotactic perception depends, is as yet entirely un- 

 known. We are ignorant whether the cilia only are the perceptive organs — as 

 is possible ; if so, then, in a strophic reaction, it is obviously due to dissimilar 

 concentrations of the solution affecting opposite sides of the cilia. Since, how- 

 ever, the cilia must by their movements neutralize differences of concentration 

 in the fluid, this view does not appear to us to be correct and we prefer to adhere 

 to the hypothesis already formulated, viz. that it is the difference in concentra- 

 tion, anteriorly and posteriorly, that is appreciated. Further, we are ignorant, 

 whether it is necessary that the stimulant must actually enter the organism 

 before a chemotactica stimulus can be produced, since, as Pfeffer (1888) has 

 shown, it may also operate by contact, i. e by merely striking against the pro- 

 toplasmatic layer. It is more probable, however, that these bodies enter the 

 cell and induce chemical changes in its interior. 



It has been already several times pointed out that the osmotic pressure 

 of the solution acts as a stimulus on motile organisms {osmotaxis). Proof of this 

 fact has been advanced by Massart (1889). If Spirillum undula and Bacterium 

 megatherium be submitted to the attractive influence of a very dilute (0-0005 G.M.) 

 solution of potassium carbonate placed in a capillary tube, the positive chemo- 

 taxis may be counteracted by the addition of various substances, and it would 

 appear that the repulsive effect then depends only on the osmotic pressure of 

 these bodies and not on their chemical constitution. Materials with an isosmotic 

 coefficient = 3, such as ammonium chloride, sodium chloride, potassium chloride, 

 &c., initiate a repulsive reaction when the concentration =0-07 G.M., while sub- 

 stances with 4 as their coefficient induce it at a concentration of 0-05 G.M. to 

 o-o6G.M, Exceptions are undoubtedly known, but these may be readily ex- 

 plained. Since, e.g., potassium and sodium oxalates or potassium cyanide act 

 repulsively at all concentrations which have been experimented with, the action 

 is not osmotic but chemical. The same result takes place when certain good 

 nutrients act as attractive agents, even when in a high state of concentration, 



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