METHODS OF PHYSIOLOGICAL ANALYSIS 77 



sions. With low concentrations of methylene blue the entoplasm of Para- 

 mecium stains before the ectoplasm, and the posterior before the anterior 

 ectoplasm. With a certain higher range of concentrations ectoplasm and 

 entoplasm stain about equally. With still higher concentrations ecto- 

 plasm stains before entoplasm, and anterior ectoplasm finally becomes 

 more deeply stained than posterior (Child, 19346). Other protozoa show 

 similar relations, and in metazoa staining gradients in opposite directions 

 along an axis have been observed with low and high concentrations of dye. 

 Even when earlier stages of staining are quite uniform along an axis, as far 

 as can be determined, a very distinct gradient in depth of staining and in 

 toxic or lethal effect appears later. This susceptibility gradient evidently 

 results from difference in condition inside the cells and a consequent differ- 

 ence in adsorption or combination of the dye, rather than from any differ- 

 ence in permeability. Experiments with Paramecium on penetration of 

 ammonia and acetic acid and with hydroids, using neutral red as indicator, 

 have shown some evidences of an axial differential permeability to ex- 

 tremely low concentrations. '■• These concentrations, however, are only 

 shghtly or not appreciably toxic; and with the higher concentrations, in 

 which a lethal gradient appears, penetration seems to occur equally at all 

 levels. Strong bases and strong acids do not alter the color of the intracel- 

 lular neutral red until cytolysis begins, but the death gradient is the same 

 as with weak bases and acids. A very distinct susceptibiUty gradient ap- 

 pears in single elongated cells of monosiphonous algae, even though no 

 difference in penetration or depth of staining can be observed (Child, 

 1916c, e, 1917a, 1919/). 



ELECTRIC POTENTIAL DIFFERENCES 



For many years electric potential differences and their changes with 

 activity have been investigated in nerve and muscle, and numerous ob- 

 servations have been made on other organs of plants and animals. Most 

 of these investigations, however, have been on organs of fully developed 

 individuals, and the work on nerve and muscle has been concerned very 

 largely with vertebrate material. These investigations, important as they 

 are, are only remotely connected with problems of developmental pattern. 

 Potential difference in relation to developmental pattern and physiologi- 

 cal axes has received less attention, but data on axial potentials in certain 



'I Child and Devincy, 1926; Child, ig2ba, and unpublished data. 



