METHODS OF PHYSIOLOGICAL ANALYSIS 67 



with methylene blue and some other basic dyes in several algae, hydroid 

 planulae and later stages, and other invertebrates (Child). 



Methylene blue is known to increase respiration in tissues of higher ani- 

 mals and to protect against the action of cyanide. '^ Whether the reversal 

 of the susceptibility gradient to cyanide by dyes is due to increased respi- 

 ration of the more deeply stained regions, which antagonizes the action of 

 cyanide, or to decreased respiration resulting from injury by the dye, and 

 consequently decreased susceptibility to cyanide, has not been deter- 

 mined. 



Recently differences in vital staining of regions and blastomeres in cer- 

 tain eggs and embryos have been interpreted as evidences of differentia- 

 tion. In the absence of information concerning technique, concentrations 

 used, periods of staining, and toxic effects of the dyes used, it is perhaps 

 questionable whether some of the differences described— for example, in 

 cleavage stages — are not due to other factors than differentiation." Deep 

 staining of one cell earlier than others about it may in some cases indicate 

 only greater susceptibility and earlier injury by the dye, possibly in con- 

 nection with certain stages of the division cycle. Some basic dyes are 

 much more toxic than others; but, in general, intracellular accumulation 

 of dye beyond a certain point results in injury to the protoplasm, and with 

 further staining cytolysis and death occur. The graded differences in 

 these effects along physiological axes of many organisms suggest quanti- 

 tative, rather than specific, regional differences, but they do not exclude 

 the possibility that specific differences are present without effect on dye 

 action or that the staining characteristics of certain cells or organs may be 

 associated with their differentiation. It appears beyond question, how- 

 ever, that use of a wide range of dye concentrations and staining periods is 

 necessary as a basis for conclusions concerning the significance of differ- 

 ences in staining. 



DIFFERENTIAL REDUCTION AND OXIDATION 

 OF VITAL DYES 



Intracellular reduction with change or loss of color of certain vital dyes 

 occurs under anaerobic conditions or when oxygen tension of the medium 

 falls below a certain point. The oxygen-level at which reduction of a par- 



»See, e.g., Eddy, 1931; Gerard, 1932, pp. 504-7; M. M. Brooks, 1932, 1935; Chen, Rose, 

 and Clowes, 1933; Marsh, 1934; Solandt ei al., 1934; Chrisler, 1935; Bodine and Boell, 1937, 

 and citations by these authors. 



" Ries, 1936, 1937; Ries and Scholzel, 1934; Ries and Gersch, 1936; Gersch and Ries, 1937. 



