SUMMARY OF THE CHAPTER 45 



a while to the action of a certain stimulating agent respond no 

 longer to a concentration which would at first have provoked 

 a reaction. In both cases it is the action of the chemical agent 

 which modifies the subsequent action of the protoplasm, without 

 doubt by changing the chemical constitution of the protoplasm. 



Mechanics of Response. — Having considered the general 

 relation between strength of stimulus and of reaction, it now 

 becomes necessary to examine more in detail into the way in 

 which the reaction takes place. 



A variety of kinds of locomotion exists among chemotactic 

 organisms — that of the Myxomycetes is amoeboid, that of 

 Infusoria is by flagella or cilia. In all cases the first and 

 perhaps the only effect of the acting reagent is to determine 

 the position of the axis of the body, in the case of bodies with 

 fixed form ; or to determine the pole, of outflow in the case of 

 amoeboid organisms. The axis lies in the line of flow of the 

 diffusing solution or perpendicular to the isotonic lines, or lines 

 of equal concentration. Whatever movement now occurs must 

 be either towards or from the source of stimulus. 



I have said above that the axis orientation is perhaps the 

 only effect of the acting reagent. Pfeffbr ('84, p. 463 ; '88, 

 p. 631), indeed, maintains that the stimulus does not directly 

 cause a markedly more rapid locomotion in the case of bacteria 

 and Flagellata ; but in the case of plasmodia it seems possible 

 that such a hastening of movements occurs. (Stahl, '84.) 

 However, it is necessary that measurements should be made in 

 this matter. Further observations on the mechanics of taxis 

 must be deferred to the general treatment of the subject in 

 Chapter IX. 



Summary of the Chapter 



We attempted in the first section to bring together observa- 

 tions relating to the action of various chemical substances upon 

 protoplasm with the aims of discovering the general laws of 

 poison-action on protoplasm and of gaining an insight into the 

 chemical structure of protoplasm and the chemical operations 

 involved in the elementary vital processes. We ought now, 

 therefore, to attempt to draw such conclusions as the imperfect 

 and often confusing data we have collected will permit. 



