82 GROWTH AND MORPHOGENESIS 



amphibian gastrulae can be found in our vital staining experiments 

 of 1950. When ectoblast fragments or chordoblast fragments of a 

 young gastrula are placed in neutral red for some time, only the 

 cytoplasmic granules (yolk platelets, pigment, mitochondria and 

 microsomes) are stained. If such a stained fragment is placed in 

 contact by its internal face with an unstained piece, they both stick 

 together and the superficial layer of the unstained fragment quickly 

 becomes coloured. Interposition of a cellophane membrane (which 

 does not prevent diffusion of free neutral red) completely suppresses 

 the diffusion of the dye from the stained fragment to the other one. 

 The embryological interest of these observations is somewhat 

 decreased by the fact that staining is possible in both directions; 

 stained ectoderm as well as stained organizer can be used for such 

 experiments. 



These experiments also suffer from the fact that neutral red is of 

 course not a natural constituent of living cells and that its use might 

 lead to a very artificial situation and thus to misleading conclusions. 

 It is for this reason that similar experiments have been performed by 

 Ficq (1954a) with radio-isotopes as markers and an autoradiography 

 technique for detection. By grafting into a normal gastrula an 

 organizer in which either RNA or proteins had previously been 

 labeled, appreciable radioactivity was found in the induced neural 

 tube. The experiments suggest a passage of intact ribonucleoproteins 

 from the organizer into the induced tissue. Unfortunately, the 

 primary neural tube of the host also had measurable radioactivity. 

 This observation indicates that part of the radioactive material is 

 broken down (perhaps as a result of limited cytolysis in the im- 

 planted organizer) and re-utilized by the host's neural tube. Similar 

 results have been obtained in Waddington's laboratory by several 

 workers (Waddington and Sirlin, 1955; Sirlin et ah, 1956; Pante- 

 louris and Mulherkar, 1957). They conclude that there is no large 

 scale diffusion of macromolecules from the organizer to the in- 

 duced tissues during induction. Their autoradiography experiments, 

 however, cannot exclude a passage of ribonucleoprotein macro- 

 molecules from the inducer to the reacting cells, but this can only 

 occur on a small scale. 



