92 THE ORIGIN OF LIFE 



ance of the colloid was greatly altered, as it 

 became intensely opaque. 



Bouillon, which was carefully sterilised, under 

 pressure, with radium at a temperature from 130° 

 to 140° cent., for about thirty minutes at a time, 

 was also tried. It was found in this case that 

 after two days a culture grew on the surface of 

 the gelatin. Moreover, on repeating the experi- 

 ment it was observed that the culture, if it might 

 be so called, was still formed, even when the tube 

 was not frozen. 



This was most remarkable, but the obvious 

 explanation appeared to be that the cultures were 

 contaminations and the result of imperfect sterilisa- 

 tion. So the experiment was repeated with con- 

 trols. The result was precisely the same as before 

 obtained in the tube containing radium, whilst the 

 control tube showed no sign whatever of con- 

 tamination. The radium was mixed with the 

 gelatin medium in most of the experiments ; in 

 some, however, it was contained in another and 

 smaller tube close to the surface of the gelatin, 

 or in a side tube. In all the experiments which 

 may be regarded as reliable, actual contact seemed 

 to be necessary, although at first it seemed as 

 though the a-rays were sufficient. In all such 

 cases some of the radium actually reached the 

 gelatin during the process of sterilisation. 



In the earlier experiments the salt used was 

 the chloride. It was sprinkled on a narrow glass 

 slide over which a thin layer of gum was spread. 



