August 19, 1904.] 



SCIENCE. 



247 



On the other hand Van Beuren and Zinsser,* 

 as a result of a small number of experiments, 

 were unable to ascribe with certainty any bac- 

 tericidal properties to radium, and explained 

 the few cases in which harmful action seemed 

 to have resulted as due to the experimental 

 error of the methods employed. 



At the suggestion, and through the kindness, 

 of Dr. Francis H. Williams, of Boston, who 

 has employed radium in practice with marked 

 success, I was recently enabled to make, under 

 favorable conditions, some experiments to de- 

 termine the eflfect, if any, of a brief exposure 

 to radium rays of two well known species of 

 bacteria (the coromon intestinal bacillus and 

 the bacillus of diphtheria), and one blastomy- 

 cetous fungus (yeast). 



The radium salt used in my experiment was 

 the pure bromide having an estimated radio- 

 activity of 1,500,000 units. This salt emits 

 three distinct sets of rays,, known respectively 

 as the alpha, the beta and the gamma rays. 

 Of these the alpha rays are lacking in power 

 and are readily absorbed by most substances, 

 as, for example, by a mica plate, or a sheet of 

 paper, so that they are without special interest 

 in this connection. The beta rays are ab- 

 sorbed by certain substances, aluminium, for 

 example, but if not cut off by these may be 

 active at short distances, perhaps within five 

 centimeters. The gamma rays are active at 

 greater distances, even up to several meters, 

 and are not readily absorbed. The number 

 of gamma rays to beta rays is about one to 

 fifteen. 



It is easy to observe the combined action of 

 the beta and gamma rays by exposing a cul- 

 ture of micro-organisms at a short distance 

 from the radium, and the effect of gamma 

 rays alone can be determined by interposing 

 an aluminium screen of about one eighth inch 

 in thickness. In my experiments the radium 

 was enclosed in a metallic capsule closed on 

 the upper side with a thin mica plate, and the 

 whole was then covered by stretching over it 

 a thin coat of rubber. Neither beta nor 

 gamma rays were thus intercepted. 



♦Van Beuren, F., and Zinsser, H., 'Some Ex- 

 periments with Radium on Bacteria,' American 

 Medicine, December, 1903. 



The first series of experiments was made 

 upon the intestinal bacillus (B. coli), this be- 

 ing taken as a typical nonspore-forming or- 

 ganism, comparatively sensitive to environ- 

 mental conditions. Active bacteria from 

 streak cultures twenty-four to forty-eight 

 hours old were inoculated into freshly poured 

 agar plates. In some cases the organisms 

 were spread out in thin surface films forming 

 spots perhaps 5 cm. in diameter, while in other 

 cases intersecting lines were drawn upon the 

 surface of the agar with an infected needle. 

 The plate cultures thus prepared were then 

 exposed to the action of radium rays for dif- 

 ferent length of time, and at various short 

 distances. 



The radium capsule was fixed, mica-side up- 

 permost, on a sterilized plate-glass table, and 

 a plate culture, the cover having been re- 

 moved, was inverted above it, and so placed 

 that the infected area was exactly over and 

 near the mica window. Protection from dust 

 was secured by covering with a sterilized 

 glass bell- jar. After the exposure the cultures 

 were removed, their covers replaced, and 

 the bacteria incubated for twelve to twenty - 

 four hours at 37°. Control plates were made 

 in every case, and the two sets were carefully 

 examined, the general and microscopical ap- 

 pearance of the cultures, and the culture char- 

 acteristics being noted. 



At the outset brief exposures were made at 

 distances of one and two centimeters. These 

 having failed to show that the radium had any 

 inhibitory or deleterious effect, the time of ex- 

 posure was gradually increased in later experi- 

 ments and the distance restricted to one centi- 

 meter or slightly less. Careful scrutiny failed 

 to show that the radiiim had any harmful 



