460 REPORT — 1 893. 



Richardson's culture medium (urine) during insolation, and that this 

 insolated urine possessed antiseptic properties. In this respect Richard- 

 son's experiments confirm certain previous observations made by Roux, 

 ;but are in opposition to those of all other investigators who have devoted 

 tittention to this point. Thus Roux found that by the insolation of broth 

 in the presence of air it became unfit for the germination of anthrax 

 spores. Several other investigators, including Panzini and Janowski, 

 have repeated this experiment with different culture materials, but have 

 ■failed to confirm it. Roux's results were, however, so very definite that 

 it has always seemed to me impossible to doubt their accuracy, and I 

 have attributed the discrepancy between his results and those of others 

 to some difference in the conditions under which the experiments were 

 made. The definite proof which has now been furnished by Richardson 

 that peroxide of hydrogen is formed in some culture media by insolation, 

 and that the conditions necessary for the formation and preservation of 

 this antiseptic substance are by no means perfectly understood, cleai'ly 

 shows that Roux and his opponents may both be right, and that the 

 different results arrived at depend upon differences in the conditions under 

 which the experiments were carried out, the nature of which differences 

 is at present not understood. That Roux's insolated broth was rendered 

 unfit for the germination of anthrax spores by the presence of peroxide of 

 hydrogen is almost certain also from the fact that he found such insolated 

 broth to recover its original nutritive properties if it was kept in the dark 

 or in diffused daylight for a certain length of time. 



2. The proof of the formation of peroxide of hydrogen during 

 insolation naturally suggests the question whether the whole bactericidal 

 effect of light is due to this material, or whether it only partially accounts 

 for the phenomenon. This important question is one which it is far from 

 easy to answer owing to the almost insuperable difficulty of securing 

 conditions under which the generation of peroxide of hydrogen is 

 impossible. We will examine some of the expei-iments which bear on 

 this point : — 



(a) Downes and Blunt foand that germs which had been air-dried on 

 glass were destroyed by subsequent insolation. 



(b) Moment found that anthrax spores dried fw twelve hours by means 

 of a sulphuric acid vacuum subsequently withstood insolation for upwards 

 of 100 hours. 



(c) Marshall Ward dried anthrax spores on glass at 70° C, and 

 found that they were subsequently rapidly destroyed by insolation. 



In none of these three sets of experiments can the conditions be 

 regarded as precluding the possibility of the formation of peroxide of 

 hydrogen. Moisture must certainly have been present in Downes' and 

 Blunt's experiments, and in smaller quantity in Marshall Ward's. In 

 Moment's experiments the desiccation was doubtless the most complete, 

 and at first sight the long insolation endured by his desiccated spores is 

 very significant ; but I do not regard it as wholly conclusive owing to 

 the impossibility of comparing the deportment of spores of different 

 origin, and also to the fact that Moment used the more delicate method 

 of detecting their vitality — viz., subsequent cultivation in broth — whilst 

 Marshall Ward used, I believe, agar or gelatin ; and Downes and Blunt, 

 Pasteur solution — culture media which are not as sensitive as broth. 



There are other experiments, again, which bear upon the same subject. 

 Thus Richardson has shown that the formation of peroxide of hydrogen 



