THE MECHANISM OE LIFE 497 



time expressing to which of the two biotonic series c and c belong. 

 The conditions that exist in a resting cell at the two different 

 parts of the body can then be represented as follows : 



c 

 m which - expresses the relation of contraction to expansion 



that prevails at the two opposite poles of the organism. 



In a cell in which c and e are equal and an equal tendency 

 toward contraction and expansion exists upon all sides, no move- 

 ment can take place in any direction. But this is at once changed, 

 when differences in biotonus appear at two points upon the sur- 

 face, when c or c under the influence of a stimulus acting uni- 

 laterall}' becomes greater or smaller at one pole than at the other. 

 Then a cause is afforded for a unilateral movement. 



Since the remarkable phenomena of chemotaxis, barotaxis, 

 thermotaxis, phototaxis and galvanotaxis are even now often 

 considered as mysterious " attractions " and " repulsions " of 

 unicellular organisms proceeding from the source of the stimulus, 

 the origin of which thus far it has not been possible to explain 

 mechanically, it is of great interest to see how their mechanism 

 follows with absolute necessity from the special kinds of motion of 

 each form of cell as the result of polar differences in the biotonus. 

 Such a fact is of more interest because many of the phenomena 

 mentioned, especially the chemotaxis of Bacteria and leucocytes, are 

 of far-reaching significance in the pathology of the human body. 



If the following three factors be considered, namely, the special 

 modes of motion of an}' organism (protoplasmic, flagellar, ciliary 

 motion, etc.), the change of this motion under the influence of 

 stimuli, and the part of the body in which with unilateral stimu- 

 lation the effect in each case is localized, the mechanism of these 

 tactic phenomena, impressive because of their exactness, will appear 

 very simple to any one who is accustomed to the study of motile 

 mechanisms. 



Let us imagine a unicellular organism, which is longitudinally 

 differentiated, moving undisturbed in a desired direction through 

 the medium in which it exists, and then suddenly affected upon 

 one side by a stimulus. It is a general rule that all iiniaxially dif- 

 ferentiated organisms move in the direction of their long axis. 

 Hence, in order to approach toward or remove from the source of 

 the stimulus, it would be necessary for the stimulated organism 

 first to assume a definite position with reference to its longitudinal 

 axis, so that it would direct its anterior or its posterior pole toward 

 the source of the stimulus. If this axial position be once assumed, 

 a movement toward or away from the source of the stimulus must 

 at once take place by the usual method of locomotion, while the 

 further action of the stimulus prevents or corrects occasional devia- 



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