76 



THE CELL AND PROTOPLASM 



ethyl alcohol and with certain ranges of 

 increased and decreased hydrozer-ion con- 

 centration, differential conditioning and re- 

 covery occur rapidly; with cyanide and 

 many other agents, more slowly. Fre- 

 quently when a certain region is inhibited 

 in early stages of development, an organ 

 which would normally develop from it de- 

 velops from a less inhibited region; with 

 differential conditioning or recovery an 

 organ may involve other cells in addition 

 to those normally concerned. 



With progress of development new gra- 

 dient patterns or systems appear in definite 

 relation to the earlier patterns. These 

 doubtless differ as from earlier gradients, 

 as regards character of reactions, but 

 within each such system the differences are 

 probably at first predominantly quantita- 

 tive and differential modifications are pos- 

 sible. Later specific differentiations may 

 appear in relation to the gradient pattern. 

 Various axiate organs apparently follow 

 some such course of development. They 

 arise at a certain level of a more general 

 gradient pattern, often as buds in which 

 we can find nothing but a quantitative 

 gradient pattern decreasing from a center, 

 and later differentiation may occur within 

 this pattern, but until it has attained a 



certain stage its course is alterable by 

 external factors. 



In conclusion, it may be suggested that 

 organismic patterns, whether of a single 

 cell or a multicellular system, represent in 

 origin the most general behavior patterns 

 of living protoplasms, their most general 

 responses to environmental factors, either 

 external or within other organisms. Even 

 in those cases of fission in Protozoa and 

 Metazoa and of reconstitution of pieces iso- 

 lated by section in which a part of the 

 parental pattern becomes the basis for de- 

 velopment of the new pattern, the partial 

 pattern is altered by the altered conditions 

 associated with fission or experimental iso- 

 lation of the piece. Moreover, we know 

 that it can be further altered experi- 

 mentally in many cases. As noted above, 

 it is now generally held that embryonic 

 developmental pattern originates in rela- 

 tion to environmental factors within the 

 parent organism, and it, too, can be modi- 

 fied experimentally. According to this 

 view, the organism itself and the differ- 

 entiations of its cells represent behavior 

 of living protoplasms no less truly than 

 do the reactions of the adult organism 

 which the patterns of differentiation make 

 possible. 



