Ill 



XENO-INDUGTIONS 



437 



material tested was the tobacco-mosaic virus, which, as was expected, lost much 

 of its activity after treatment with ribonuclease. When Kuusi (1951) observed 

 that this enzyme did not appreciably reduce the inductive capacity of several 

 active parts of xeno-inductors, she repeated the experiment with the same virus, 

 hydrolyzing the RNA with perchloric acid, but did not observe a decrease of its 

 inductive power (Kuusi, 1953). The discrepancy was attributed to possible 

 proteolytic impurities in the ribonuclease previously used by Brachet. 



Fig. 88. Comparison of the induction frequencies obtained with the ribonuclein (RNP) 

 extract of guinea pig liver. In series E the inductor was the homogenate precipitated by 

 ethanol. In series PT, the extract was submitted to precipitation by streptomycin sulfate 

 and further purifications to obtain the RNP precipitate. In series SP the supernatant 

 obtained after precipitation by streptomycin was dialyzed under definite conditions 

 (pH 7.6) and precipitated by ethanol. In each group: white column, frequency of optic 

 vesicles; hatched column, acrencephalon; dotted, olfactory placodes; black, mesenchyme. 

 The greater frequency of acrencephalic structures in series PT is manifest. From Hayashi, 



1956. 



Other results, however, still hinted that nucleic acids played a positive role: 

 H. Lehmann (1938) obtained inductions with the DNA-containing fraction of 

 pancreas, thymus, and liver; Brachet, Kuusi and Gothic (1952) got inductions, 

 mainly acrencephalic, with cell-nuclei of rat, guinea-pig, pigeon liver, and thymus 

 nucleo-histone, but were for the most part unsuccessful with injections of fresh 

 liver microsomes, due probably to the small quantity of inductor. Kuusi (1953) 

 obtained positive results with nucleoli of star-fish oocytes, commercial RNA, 

 RNA from rabbit liver microsomes and from guinea pig kidney. Still other results 

 pleaded in the opposite direction. Yamada, Takata and Osawa (1954) proceeded 

 to the isolation of the RNA contained in guinea-pig liver homogenates but did 

 not obtain really positive results, except in cases when cytolysis was suspected. 

 Saxen and Toivonen (1957) compared the inductive effect of rat liver either 

 normal or taken in phase of full regeneration, when much richer in RNA. Both 

 samples have the same activity, qualitatively (acrogenic) and quantitatively. 



Literature p. 483 



