190 LIFE: ITS NATURE AND ORIGIN 



free in all tissues." This is readily understandable on the basis 

 of the catalyst mechanisms discussed below. Needham also points 

 out many resemblances in behavior between the primary organ- 

 izer and the plant hormones, auxin and "bios," which also can 

 exist in "bound" condition, show no species-specificity, and are 

 "unmasked" subtly. He also remarks that the retort of Prof. W. 

 Lash Miller to critics of Miller's and other early work on "bios", 

 "is not without moral for embryologists." Miller said: "All those 

 who say, 'No doubt some chemical in the wort makes all the dif- 

 ference, but it need not be Bios', have qualified to join the Last 

 Ditch Bacon Club, which holds that Shakespeare's plays were 

 written, not by Shakespeare, but by some other person bearing 

 the same name." 



The Chemical Nature of the Primary Organizer 



By use of various solvents and precipitants, fractions acting as 

 organizers have been prepared; but as their inductive capacities 

 vary with the treatments, it may be that the organizer consists of 

 more than one substance or else becomes altered or broken down 

 in the separation process. It seems to be of steroid nature, a view 

 supported by the work of Waddington, Needham and co-work- 

 ers. 14 



L. G. Barth 15 obtained excellent inductions of brain tissue by 

 implantation of cephalin prepared from mammalian brain. Then 

 Fischer and collaborators 16 obtained inductions of neural tubes 

 by implantation of thymonucleic acid and of adenylic acid derived 

 from muscle. Later they found both purified and synthetic oleic 

 acids to be effective, as well as linolenic and octadecenic acids 

 and nucleo-protein from calf thymus; so they believed that acid 

 stimulation is responsible, a concept which the buffer action of 

 cell groups (tissues) renders most indefinite. 



Methylene blue in high dilution causes induction. 17 Thus a 

 piece of ventral ectoderm isolated from the gastrula and cultured 

 two days in M 10 5 methylene blue nutrient induced a large brain 

 in a host, and being competent, became neuralized itself. A simi- 

 lar isolate became neuralized by longer cultivation in methylene 

 blue medium. Histochemical tests revealed in the gastrula ecto- 

 derm (the presumptive mesoderm and presumptive neural plate) 

 a substance termed "plasmogen," later found to be a phosphatide 

 in which aldehydes of higher fatty acids are combined with glyce- 

 rol, phosphoric acid and amino-ethylalcohol; it is related to the 



