TRANSACTIONS OF SECTION B. 835 



picture. The author also demonstrated that the action could pass through such 

 media as thin sheets of gelatine, celluloid, gutta-percha, collodion, &c., and that 

 even a picture of a metal surface is obtainable through such media. It was sug- 

 gested that these different phenomena could be explained on the supposition that 

 hydrogen peroxide is in all cases produced. 



3. The Action of Bacteria on the Photographic Flate. ^,y Percy Frank- 



land, Ph.D., B.Sc, F.R.S., Professor of Chemistry in Mason University 

 College, Birmingham. 



The action on the photographic plate which is exerted by uraniuui and its 

 compounds, by zinc and several other metals, as well as by a number of organic 

 substances, naturally leads to the inquiry as to whether living structures may not 

 also be endowed with the power of recording their presence by action on the 

 sensitive film of the photographer. The author has opened up this inquiry by 

 investigating the behaviour of bacterial cultures towards highly sensitive photo- 

 graphic plates. 



Gelatine cultures of the bacillus eoli communis and of proteus vulgaris were 

 found when placed at a distance of half an inch from a photographic plate to pro- 

 duce the same effect as light, the exposure lasting over nine days in absolute dark- 

 ness. Definite pictures of the bacterial cultures were obtained by placing the 

 sensitive film in actual contact with the cultivations, the exposure being extended 

 over a period of fourteen days. Similar results were obtained with agar-agar 

 cultivations. 



As this action does not take place through glass or mica, the author is of 

 opinion that it is not due to any form of radiation, but to the epolution of volatile 

 matter entering into reaction with the photographic film. As far as the author's 

 experiments have gone, the action is exerted both by bacteria which liquefy 

 {profeus ridgaris) and those which do not liquefy gelatine (6. coli communis and 

 tlie typhoid bacillus). It is, however, quite possible that considerable differences 

 in respect of this activity may be found to exist in the case of different bacteria, 

 and that this property may become of importance in their diagnosis. 



Bacterial growths which are luminous in the dark {photo-bacterium phos- 

 pliorescens) were found to exert a still more powerful action on the photographic 

 plate. 



The author proposes extending these investigations not only in connection witli 

 bacteria but also in respect to other organised structures, vegetable and animal, 

 living and dead. 



4. Further Experiments on the Ahsoiytion of the Rontgen Rays hy 



Chemical Compounds. By J. H. Gladstone, D.Sc, F.R.S., and 

 Walter Hibbert. 



At the two previous meetings of the British A.ssociation the authors had ex- 

 amined the absorption of Rontgen rays, especially bj" metals and metallic salts. 

 During the past year they have endeavoured to perfect the quantitative method.s 

 employed for estimating the comparative intensity of radiographs taken simulta- 

 neously ; and to determine whether the amount of absorption is purely' an atomic 

 phenomenon, or whether the amount of rays absorbed by a compound body depends 

 to any extent on its physical condition or manner of combination. 



In the experiments recorded the authors had again employed the Lummer- 

 Brodhun photometer ; and had endeavoured to get rid of irregularities of exposure 

 by placing the objects simultaneously exposed to be radiographed at a considerable 

 distance from the radiating point (averaging 15 or 16 inches), and rotating them 

 during the experiment. They believe that in this way the effect upon the sensitive 

 plates can be determined within ± 2 per cent. An experiment was usually 

 repeated about six times, and the mean taken. 



Among the results arrived at were the following. Finely-pounded glass gave 



3 H 2 



