478 PATTERNS AND PROBLEMS OF DEVELOPMENT 



metabolic activity with glycogen as source; that is, the activity, rather 

 than the substance, is the real inductor. 



Other attempts were made with other methods to isolate a particular 

 inductor substance. The material of neurulae, crushed in a small volume of 

 water and centrifuged, separated into three layers — the cellular debris, an 

 aqueous layer containing protein but not entirely fat-free, and a fatty 

 layer. Induction of neural tubes was obtained by implantation of coagu- 

 lated parts of the aqueous, protein-containing layer. Also, neurulae, 

 ground with anhydrous sodium sulphate, the mass extracted with ethyl 

 ether or petroleum ether and the extract mixed with solid carriers shown 

 by experiment not to be inductors, gave, when implanted, neural tubes or, 

 more commonly, solid rods and other masses, "probably neural in char- 

 acter." Petroleum ether extracts of adult amphibian viscera were also in- 

 ductive. From these experiments the conclusion was drawn that the in- 

 ductor is a definite chemical substance, soluble in ether and probably 

 lipoidal.-^ 



Continuing work with ethereal extracts, Waddington, Needham, and 

 co-workers obtained induction in Triton and axolotl with the unsaponiti- 

 able fractions of ether extracts of whole newt bodies and mammalian liver 

 and with the parts of these fractions precipitated by digitonin, implanted 

 after emulsifying in egg albumin and coagulating by heat. Minute doses 

 of certain synthetic polycyclic hydrocarbons, massive doses of certain 

 acids, and certain other substances may also induce. Recently methylene 

 blue has also been found to induce, and it has been suggested that it acts 

 by setting free an inductor substance. Nuclei of unfertilized amphibian 

 eggs are more potent inductors than the cytoplasm. The earlier sugges- 

 tion of these workers was that induction was due to a sterol-Uke substance ; 

 but further experiment seems to indicate that, even if such substances are 

 inductors, other substances also induce.^^ The possibility that methylene 

 blue, a respiratory catalyst in certain concentrations, induces directly by 

 activation may be noted. Methylene blue in low concentrations increases 

 oxygen uptake 45 per cent in amphibian embryos, in high concentrations 

 is inhibitory ; and Janus green and neutral red in low concentrations also 



"^ Waddington, Needham, and Needham, 19330, b; Needham, Waddington, and Needham, 

 1934- 



^'Waddington, Needham, ei al., 1934, 1935; Waddington and D. M. Needham, 1935; 

 Waddington, Needham, et al., 1936; Waddington, Needham, and J. Brachet, 1936; Wadding- 

 ton, 1938a, b. For a quantitative study of induction by a water-soluble hydrocarbon see 

 Shen, 1939. See also Needham, 1939, "Biochemical aspects of organizer phenomena," Groictli, 

 Suppl. 



