64 PATTERNS AND PROBLEMS OF DEVELOPMENT 



the color gradient appears only gradually. If any permeability gradient 

 were originally present, it is probably destroyed at once.^ 



DIFFERENTIAL INTRACELLULAR INDOPHENOL REACTION 



The indophenol blue reaction between a-naphthol and dimethyl-para- 

 phenylenediamine, which is catalyzed by certain oxidases, has been used 

 with various ciliate protozoa, embryonic and larval stages, and small ani- 

 mals, also in certain experiments on reconstitution. A very distinct axi- 

 al gradient in appearance within the cell or cells of the indophenol blue 

 color is characteristic of the living animal, but none or only traces for a 

 short time if the organisms are first killed. The reagents must be used 

 in extremely dilute solutions, to avoid killing. The extensive litera- 

 ture on the indophenol reaction, the indophenol oxidase or oxidases, and 

 their relation to tissue oxidation and respiration need not concern us here. 

 It has been shown that dimethyl-paraphenylenediamine increases oxygen 

 consumption in certain tissues and that a-naphthol inhibits oxidations. 

 Moreover, not all the oxidation products of paraphenylencdiamine give 

 indophenol blue with a-naphthol, and it may happen that the more vigor- 

 ous the oxidation, the less blue is formed. Also, indophenol blue may be 

 decolorized by the reducing action of certain tissues. The greater part of 

 the work with this reaction has been done with vertebrate tissues, and it 

 is by no means certain that the conclusions and hypotheses based on it 

 hold without modification for the lower invertebrates, embryonic tissues, 

 and unicellular organisms. 



Attempts have been made with hydroid planulae and starfish blastulae 

 and gastrulae to determine whether or to what extent differential perme- 

 ability to the agents might be concerned. The material was placed first 

 in one of the agents for one to several minutes, then in the other. It was 

 found that with this procedure both agents, in the very low concentrations 

 used, were present in all parts of the material within a short time in suffi- 

 cient quantity to give the same reaction as with much longer exposure. 

 Five minutes or less was sufficient for complete penetration of either re- 

 agent, but difference in time of the reaction along a polar axis may be an 

 hour or more. That the indophenol gradient indicates an axial physiologi- 

 cal differential of some sort is evident; that it indicates a differential as- 

 sociated with indophenol oxidase appears highly probable; and that it 



5 For use of KMn04 in this way and results obtained see Child, 1919a,/, 1921a, 1925a, 

 1926a; Hyman, ig2ob; Galighcr, 1921a. 



