478 GERMINAL ORGANIZATION INDUCTION PHENOMENA 4 



act on the reactor (Brachet [1955, 1957] for example has demonstrated the degree 

 of the disturbance caused by ribonuclease). Generally speaking, trypsin, chymo- 

 trypsin, and both nucleases reduce or suppress the inductive power. "A conclusion 

 that might be drawn from these experiments in that induction in torosus and 

 axolotl by the conditioned medium is due mainly to ribonucleic acid, somewhat 

 to desoxyribonucleic acid, but not to protein". This conclusion has led his author 

 (Niu, 1958) to isolate from veal kidney, liver and thymus their ribonucleo- 

 proteins and their RNA, and to test the influence of this RNA on component 

 ectoblast. To obtain a plain differentiation, the cultures were grafted on the flank 

 of older embryos. In 25 to 40% of cases, a pattern of differentiation corresponding 

 to the origin of RNA was observed. The frequency was increased if some protein 

 was added to the culture medium. 



Coming back to the nature of the primary inductor, our representation remains, 

 after this elaborate discussion, that it is linked with a gradient field of some ribo- 

 nucleoproteins endowed with notogenic properties. With the final period of 

 segmentation they undergo, in the areas of greater concentration, a gradual 

 conversion into smaller, more easily transmissible and more stable molecules, a 

 conversion taking place at the highest rate in the primordium of the prechordal 

 plate, at a lesser and decreasing rate in the primordia of the notomerit. Owing to 

 the definite characters of the various secondary inductions, and organs, it may 

 be assumed that the primary agents undergo a further modification, adapted 

 to each case, in order to become the secondary and tertiary inductors. 



It is also not excluded that these populations of specialized molecules would 

 persist in the organs throughout the life of the individual, but, so far, they did 

 escape detection. The idea is neither new nor obsolete that such components, 

 influencing cell proliferation, differentiation and normal growth could, through 

 abnormal transformation, be at the origin of malignant growth (see Holtfreter, 

 1948). This is of course a prominent reason to wish further advances in this 

 intriguing field. 



Assuming that these views are sound, a few comments may be introduced here 

 in favor of the concept or organizing which Pasteels and myself proposed twenty 

 years ago. If the primary morphogenetic field of pregastrular stages is actually 

 due to some ribonucleoprotein which is partly transformed during gastrulation 

 into a somewhat different compound according to the scheme developed above, 

 and if other modulations of the molecular structure soon follow, it seems convenient 

 to use the term "organizin" which so clearly suggests an inductive action. Even 

 if the exact nature of some induction were soon disclosed, e.g. of the acrogenetic or 

 notogenetic one, the name of the substance will presumably be a complex one, 

 and its formula extremely complicated. It would certainly be easier to speak of 

 acro-organizin and noto-organizin, or, for more specific cases, of a neuro-, or myo-, 

 or lens-organizin. There are sufficient examples of cases where substances with 

 definite effects have been named according to their origin or function, for example, 

 adrenalin, thyroxin, secretin, insulin, folliculin, etc., before their chemical identity 



^ Lender currently used this concept in his research on the induction of eyes under the 

 influence of brain in regenerating flat-worms {cf. 1952). 



