THE AXIAL GRADIENT IX CILIATE INFUSORIA. 



C. M. CHILD. 

 FROM THE HULL ZOOLOGICAL LABORATORY, UNIVERSITY OF CHICAGO. 



The discovery of axial gradients in rate of metabolic reactions 

 in Planaria (Child '12, '130, 'i3f) and various other forms to- 

 gether with a considerable body of evidence, mostly as yet 

 unpublished, which points to a close relation between such axial 

 gradients and polarity and symmetry suggested the desirability 

 of determining whether there is any indication of the existence 

 of such axial gradients in those protozoa which possess a definite 

 morphological polarity. If an axial gradient in rate of metabolic 

 reactions is the basis of organic polarity or is in any way asso- 

 ciated with it we must expect to find such a gradient in single 

 cells where a definite stable polarity exists as well as in multi- 

 cellular axiate organisms. The results obtained with various 

 ciliates have fully justified this expectation. In all the forms 

 tested thus far evidence for the existence of an axial gradient 

 has been found. 



I. METHODS. 



In these experiments the method which I have called the direct 

 susceptibility or resistance method (Child, '136) was used, with 

 KCN as the reagent in most cases. This method is based upon 

 the fact determined by extensive experimentation, that in con- 

 centrations of the cyanides and various anesthetics which kill 

 within at most a few hours, individuals or regions with a higher 

 rate of metabolism or at least of the oxidation processes are more 

 susceptible and die earlier than those with a lower rate. 



In the experiments with ciliates concentrations were found 

 which did not kill the animals at once but permitted life to 

 continue for a period ranging from a few moments up to several 

 hours according to the concentration. The purpose in thus 

 limiting the concentrations used is first to avoid killing the 

 animals too rapidly, in which case the death and disintegration 

 of all parts may be so nearly simultaneous that a gradient if 



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