in XENO-INDUCTIONS 433 



Dialysis alone is, of course, a mild procedure. When applied to the liver, it 

 deprives the tissue of its acrogenic property and leaves a mainly notogenic 

 inductor (Toivonen, 1949; Toivonen and Saxen, 1955a, b). The same result is 

 obtained (Toivonen, 1949) by extraction with petroleum ether; however, the 

 evaporated residue does not show any activity; saponification of this residue 

 yields an inactive sterol fraction and a fatty acid fraction with slight acrogenic 

 activity, but probably through cytolytic action. Similarly, the kidney tissue 

 preserves its notogenic influence after extraction by petroleum ether, though 

 practically no spinal cord appears. These results were then tested on the corre- 

 sponding ox organs (Toivonen and Kuusi, 1948), which do not, after simple 

 treatment with ethanol, have distinct inductive effects. No qualitative change 

 could be registered after dialysis or after petroleum ether extraction, but only 

 a general lessening of inductive power. The evaporated residue gave results 

 analogous to those of guinea pig extracts. Consequently, a dissociation of these 

 inductors seems to be obtainable only when starting from organs having a priori 

 a different action. 



The lipids may be disposed of as possible induction agents. Their inactivity 

 has already been made evident by H. Lehmann (1938) and confirmed by Fujii 

 (1944). It may also be stated, tentatively, that of the two main inductors, the 

 notogenic one, especially its mesoblastic part, is less thermostable, but more 

 firmly bound to the tissue stroma, from which it cannot be separated by dialysis 

 nor by petroleum ether extraction. In contrast, the acrogenic inductor is more 

 thermostable, resistent to ethanol, and extractable by dialysis or by petroleum 

 ether (Toivonen, 1950). With many organs, the question arises if the more 

 acrogenic effect observed after the action of heat or of ethanol is due to the 

 selective destruction of the notogenic inductor or to the conversion of the latter 

 into an acrogenic factor. 



[e) Fractionation of the xeno-inductors 



Attempts to dissociate the xeno-inductors into several fractions, with the hope 

 of detecting the responsible components, have been numerous and of variable 

 efficiency. Holtfreter (1934b) tried chick embryo extract, which is indeed a 

 complex, and observed mixed effects, with a serious predominance of notogenic 

 structures. Recently, Von Woellwarth (1956) has reared ectoblastic explants in 

 a supernatant of embryonic extract sap of 9 days embryos, centrifuged at 

 25,000 g, this supernatant being used at various dilutions. Only pieces of 

 sufficiently large size react positively. They swell and elongate in a rather extra- 

 ordinary way. The induction consists of abundant mesenchyme, pigment and 

 neural structures ressembling spinal cords or even hind-brains with otocysts, 

 thus, a picture of notogenesis. This result is reminiscent of the acrogenesis 

 obtained by Shen with a water-soluble hydrocarbone. There is no doubt in 

 such case that the action has been exerted by substances dispersed in the medium, 

 and that the organization power is in the reactor itself. Further separations have 

 been performed on the embryo extract, but they will be considered later. 



It is somewhat difficult to localize correctly the inductions obtained by blasto- 

 coele implantation of dry extract pellets (Shering) of oxen prepltuitary (Mangold, 



Literature p. 48;^ 



