92 PATTERNS AND PROBLEMS OF DEVELOPMENT 



rapidly and more deeply than other regions, and cytolysis begins poste- 

 riorly, often in I or 2 minutes.^ 



Most of the observations on oxidation and reduction of dyes have been 

 made with P. caudatum. The dye-reduction gradient is even more distinct 

 in P. miiltimicronucleatum, decreasing posteriorly in uninjured animals 

 and reversed in direction when differential injury retards or abolishes re- 

 duction anteriorly. As might be expected, the continuously circulating 

 entoplasm of Paramecium shows no evidence of an intrinsic gradient, the 

 course of reduction in it being apparently determined by the ectoplasmic 

 gradient. The indophenol blue reaction (see p. 64) with highly dilute 

 reagents, so that the reaction occurs before the animals are killed, is most 

 sharply localized in the inner portion of the ectoplasm or on the boundary 

 between ectoplasm and entoplasm and decreases in rate from anterior to 

 posterior end (Child and Deviney, 1926). 



Differential susceptibility of P. caudatum to various gradually lethal 

 chemical and physical agents, as indicated by cytolysis or other changes 

 in the ectoplasm, decreases from the anterior end posteriorly, with a sec- 



=> Only the reversed reduction gradient resulting from differential injury of the ectoplasm 

 by the leucobase, with retardation or absence of reduction anteriorly, was observed by Roskin 

 and Semenoff (1933) with the use of a leucobase which was toxic, according to their own state- 

 ment. Their conclusion that reduction occurs more rapidly in the posterior region is therefore 

 mistaken. Using thionine reduced by rongalite (see p. 68) and oxidized Janus green, Gersch 

 (1937) concludes that oxidation of the leucobase occurs more rapidly anteriorly than pos- 

 teriorly in Paramecium and that reduction of the oxidized dye is more rapid posteriorly than 

 anteriorly. No data concerning concentrations used or staining periods are given, but the 

 rongalite-leucobase solution is stated to be somewhat toxic. The author concludes that oxida- 

 tion is more rapid anteriorly; reduction more rapid posteriorly. The question how oxidation 

 occurs in the anterior region without reduction or more rapid oxidation with less rapid reduc- 

 tion, and in the posterior region more rapid reduction with less rapid oxidation, is of interest in 

 connection with this conclusion. Apparently the dye- reduction gradient decreasing anteriorly, 

 as observed by Gersch, is, like that found by Roskin and Semenoff, the result of a differential 

 toxic effect decreasing from the anterior end posteriorly, with reduction most retarded or 

 absent anteriorly. (See also Kalmus, 1928.) Both the rongalite-leucobase and Janus green 

 are toxic, the latter extremely so. That it is essential to use a wide range of concentrations 

 of dye and, with oxidized dyes, different exposure periods, in order to avoid, as far as possible, 

 misleading results, is sufficiently evident from the results obtained with Paramecium. It is 

 possible to obtain both an oxidation and a reduction gradient in either direction, according 

 to concentration of leucobase or oxidized dye used and according to staining period with oxi- 

 dized dye. Only by varying the procedure sufficiently to determine which gradients most 

 nearly represent physiological condition and which are results of differential toxic effect is 

 it possible to attain an adequate basis for any conclusions. To assume that the animals are 

 uninjured because they continue to swim is not justified. The anterior ectoplasm may be so 

 injured that it is entirely unable to reduce the dye at all, while the animal is still able to swim. 

 These reversed reduction gradients in Paramecium resulting from differential toxic effect of 

 the dye are excellent examples of the differential susceptibility along the anteroposterior axis. 



