Ill XENO-INDUCTIONS 439 



(Hayashi, 1956), the other from kidney (Yamada and Takata, 1956). In both 

 cases, the fractionation procedure was described by Kutzky (1953), and consisted 

 roughly in extracting the homogenate with 0.14M NaCl for i h., centrifuging, 

 taking out the supernatant, and precipitating the ribonucleoproteins by strepto- 

 mycin sulfate. This precipitate was repeatedly redispersed in a stronger NaCl 

 solution, and collected by centrifugation, then dialyzed against the same solution, 

 and finally precipitated by ethanol. All operations were run at low temperatures. 

 For comparison, the supernatant left after precipitation by streptomycin was 

 treated approximately in the same manner. The essential results are summarized 



Fig. go. Typical induction of somites by a purified RNP extract of guinea pig kidney. From 



Yamada and Takata, 1956. 



in Table 7, which includes some analytical data. The ribonucleoprotein fraction 

 used seems quite homogeneous, more than in any other known instance. It 

 contains a large amount of RNP, about 8 times more than the richest extracts 

 considered in Table 6. This fraction seems to contain the principles responsible 

 for the most characteristic inductions. This is especially true for the liver extract 

 (Fig. 88), with which some implants develop a remarkably typical effect (Fig. 89). 

 The kidney extract shows a more varied picture, though also typical in the 

 majority of cases (Fig. 90, 91). For some structures, like somites and spinal cord, 

 it seems that all the active factors have not yet been extracted. Thus, in these 

 two joint experiments, the role of ribonucleoproteins is firmly established, but 

 it remains to be seen if the ribosenucleic acid — -or the protein — moiety would be 

 the active part of the isolated compound, and if the RNP is also the prevailing 

 factor in other xeno-inductors. Here we are again endebted to the Nagoya 

 laboratory for important results, which we shall still have to consider in the light 

 of bacterial xeno-inductions obtained at Koln. 



Examining more closely his guinea-pig liver extract, Hayashi (1958) has found that 

 exhaustive defatting of the sample almost preserved its morphogenetic activity, as did 

 also its treatment with ribonuclease, removing most of the RNA. Treatment of the RNP 

 sample with 0,1% pepsin at pn 4.0 during 30 min. reduced the eye frequency and increased 

 the mesenchyme frequency. With 60 and 120 min. treatments, a reduction or a suppression 



Literature f>. 483 



