729 



with regard to their action. Prof. H. Haga was willing to under- 

 take the radiogram experiments at our request, of which the results 

 were as follows: The experiments were made in the usual way in 

 which the photographic plate in a black envelope is exposed to the 

 action of the substance to be investigated ; in order to be able to 

 state an eventual action some parts of the plate were protected by 

 placing some small metal discs on the envelope, or metal pieces 

 with figures cut into them. In using "Schleussner Röntgen-plates" 

 only a very small action was obtained after a nineteen days' ex- 

 posure from Fango. Dried mud of Rockanje N°. 12 and mould 

 would have no action at all. In using "extra speedy Wellington" 

 plates a very strong etfect was obtained after a 30 hours' exposure 

 with Uranium-pitchblend, a very weak one with a strip of uranium 

 glass and no effect at all with a quantity of Rockanje mud 1913. 

 No more was any action obtained after 44 hours by strewing the 

 black envelope with the whole quantity of the last mentioned samples 

 or after a week's exposure with the above-mentioned samples from 

 Dr. Reys. The same negative result was arrived at in experiments 

 in which for a week Schleusfiner-Röntgen-plsites" vjithout the wra pper 

 had been placed over a layer of Fango or mud at ± 1 mm. distance 

 or had also been strewn with these substances. 



These results agree entirely with the photographic action on 

 radio-active substances as described in the literature on the subject. 

 In such photographic experiments one trial experiment should always 

 be taken with a plate from the same pack without any substance 

 strewn upon it, and one should always be careful with the so-called 

 black paper, some kinds of which transmit a sufficient quantity of 

 daylight to obtain a misleading effect. As the photographic experiments 

 had again given a negative result, there only remained to us to set 

 forth more clearly one side of the question. It has namely been 

 thought that there might exist a relation between organisms and 

 accumulation of radio-activity, when BtiCHNER's definitions of the 

 radio-active intensity of the Rockanje mud were known. As, accord- 

 ing to this investigator, radium probably occurs in mud as RaSO^ 

 and so many sulphur-bacteria live there, whose sulphur-reserve is 

 oxydated by respiiation, so that sulphates again are dissolved into 

 the water, it seemed desirable to us to examine bacteria-dregs and 

 watery mud from the ditch as to their activity For this purpose 

 Dr. Blaauw once more took two samples and sent them to me, 

 mixed with much water. The research tookplace both according to 

 the "direct" as well as to the emanation method. As regards the 

 latter, no emanation equilibrium was awaited, but only the quantity 



