434 GERMINAL ORGANIZATION INDUCTION PHENOMENA 4 



Tiedemann and Von Woellwarth, 1956). The effect was intense but somewhat 

 variable, with a dominant deutogenic tendency. 



From the true fractionations which have been tried with increasing success 

 during the last five or six years, two orientations have appeared as possible 

 solutions at the biochemical level: proteins and ribonucleoproteins. 



A definite hint in favor of the role of proteins was contained in the extensive 

 work of Kuusi (1951). Using guinea pig liver and kidney, she elicited character- 

 istic inductions with nucleoprotein and protein extracts. As these effects were not 

 suppressed by previous incubation of the inductors with ribonuclease, it was 

 insisted that proteins were of greater importance. This opinion was supported 

 by the considerable reduction of inductive power caused in ox liver and kidney 

 after digestion with pepsin or tripsin (Toivonen and Kuusi, 1948). 



In the same period, Yamada (1950b) used an extract of ox muscle. The ground tissue 

 was kneaded for 10 min. in 0.25% NaCl. The mixture was added with two volumes H2O, 

 then filtered and the residue macerated for some hours in o. i M Na2HP04. Centrifugation 

 yielded a supernatant which coagulated at 80" C, and dessicated by heating. The reactions 

 obtained in ectoblast sandwiches were exclusively of acrencephalic type. Since iron powder 

 was added to most of the explants, a participation of cytolysis can be suspected. However, 

 in one series without this noxious ingredient, the reactions, though less numerous, remained 

 of the same type. It may be remarked that the extract used was far from containing 

 exclusively proteins, and especially that ribonucleoproteins were certainly also present. 

 This paper is, however, quite important owing to the biochemical orientation and to its 

 theoretical discussion, which included the concept of dorso-ventral and cephalo-caudal 

 potentials and of their mediators (p. 471). 



An important advance in the same direction is represented by the attempt of Yamada 

 and Takata (1955) to explore the successive steps of fractionation of the guinea-pig kidney. 

 Samples were obtained by fundamentally following the technique of Kerr and Seraidarian 

 (1949). The homogenate was extracted at low temperature in 0.14 M NaCl, centrifuged, 

 either redissolved at neutral pn or partly precipitated by acidification, and, according 

 to the case, finally either coagulated by heat or precipitated (from supernatants) by 70% 

 ethanol. This last step was always followed by a thorough washing in standard saline 

 solution. Due attention was given to the time of preservation (at 5" C) of the specimens, 

 which turned out to be a rather important factor. This procedure has been paralleled 

 by manipulating as much of the same incipient extract as necessary to separate the ribo- 

 nucleoprotein fraction (see infra). Leaving out some infrequent manifestations not attribu- 

 table to a definite region, the results are summarized in Table 6. 



This complex but valuable enquiry brings us several pieces of new information. 

 Firstly, it makes apparent a previously undescribed modality of experimental 

 induction i.e. a quite elongated fragment containing a spinal cord and rather 

 abundant mesenchyme (Fig. 87). The authors state that in 10 cases they obtained 

 a spinal cord without either somites or notochord, but do not mention to what 

 extent mesenchyme was present; this striking reaction seems to appear sporadi- 

 cally. They insist that a deutencephalon was often observed in the absence of 

 notochord and somites, which, in my opinion, does not mean the absence of 

 any cephalic mesoblast. They also confirm the presence of notochord and somites 

 without a neural tube as obtained in the case of bone marrow. We shall interprete 

 these experimental dissociations on p. 444. Secondly, the results show that the 

 ribonucleoprotein ( = RNP) content of the inductor does not by itself command 

 the quality of the reaction; specimens 4 and 9 of Table 6 exhibit the primarily 



