PREVIOUS INVESTIGATIONS UPON PLANTS 67 



different species of Penicilliwn . Experiments with B. prodigiosus 

 and B.pyocyancus confirmed the results of Bouchard and Bahhazard. 



Dorn, Baumann, and Valentiner ^^ caused the emanation from 30 

 mg. of radium bromide (activity not given) to be bubbled through 

 sterilized bouillon for five minutes, and then added i oz. of a typhus- 

 bouillon culture. Then daily, for 10-12 days, two or three times a 

 day for ten minutes at a time, the emanation was bubbled through 

 the mixture. On the tenth and thirteenth days the cultures were 

 platted out, and in three days thereafter the exposed culture was 

 only a tenth as much developed as the control. Beta and gamma 

 rays from 5 mg. of " pure " radium bromide inhibited the growth of 

 germs of typhoid, cholera, and diphtheria. The authors hold that 

 the emanation itself, behaving as a heavy gas, has no physiological 

 effect, and their results are, therefore, to be attributed to the radio- 

 activity of the emanation. 



Guilleminot's ^ study of the comparative effects of X rays and those 

 of radium on the plant-cell were first published in November, 1907. 

 This author had previously * indicated a process for determining the 

 effectual strength of X rays, and defined a unit M, obtained by 

 a comparison of the fluorescence of barium platynocyanide and that 

 of a standard of radium. Using seeds, of Mahon's gilliflower, he 

 obtained the following results: i. The true characteristic action of 

 the rays is a retardation of growth when the strengths are rather 

 great. 2. The strength that slightly retards appears to be 3,000 M, 

 radium, and 15,000 M, X rays. 3. The fatal strength is in the 

 neighborhood of 10,000 M, radium, while 20,000 M, X rays per- 

 mits of a feeble development. 4. The accelerating action, if such 

 exists, is apparently reached at about 250-500 M, radium, and 5,000- 

 7,500 M, X rays. The differences (in result), he says, are too feeble 

 to warrant the unqualified assertion of an acceleration, and, in his 

 longer paper, he^^ states that an "exciting" dosage probably does 

 not exist. 



* Guilleminot *"' 31 adopts as a unit of intensity (M) of the field of irradiation the 

 quadruple of the intensity producing the same luminescence as a standard of 0.02 gm. 

 of radium bromide of 500,000 activity, spread over a circular surface of I cm. in diame- 

 ter, and placed at a distance of 2 cm. from the phosphorescent surface. Then the unit 

 of quantity of irradiation will be the quantity acting for one minute when the field has 

 unit of intensity. 



