172 



SCIENCE. 



[N. S. Vol. I. No. 7. 



plate made from a similar culture uot so 

 exposed. Twenty days insolation and then 

 inoculation with the typhoid bacillus 

 showed great deci'ease in the number of 

 colonies on all the plates ; some of them were 

 sterile. Insolation of fortj^ days, and inoc- 

 ulation in the same manner, gave very few 

 colonies for each plate, probably the same 

 as the number of germs introduced, i. e., 

 there had been no development. Bouillon 

 insolated 50 — 60 days and inoculated gave 

 sterile tubes. This insolated bouillon after 

 inoculation and incubation remained per- 

 fectly clear, and plates made after a week 

 of incubation gave no more colonies than 

 those made at the end of twenty-four hours. 

 Its reaction was alkaline, but not intensely 

 so. 



Insolated agar-agar — Of twenty-three tubes 

 of agar-agar insolated twenty days, and 

 then inoculated with the badlhis typhi ab- 

 dominalis, all except one remained sterile, 

 and neither the hacillus typhi abdominalis nor 

 the hacillus coli communis grew when inocu- 

 lated in stripes on these plates. Of seven 

 tubes of agar-agar insolated forty days and 

 then inoculated with the bacillus of typhoid, 

 all remained sterile. On four of these plates 

 mould appeared after some days. Of seven 

 tubes of agar-agar insolated forty days and 

 then inoculated and incubated as before, all 

 remained sterile. 



Insolated gelatine. — Of ten gelatine tubes 

 insolated forty days and then inoculated 

 with the hacillus typhi abdominalis, six re- 

 mained sterile, two contained a few colonies 

 of bacillus typhi abdominalis, and two were 

 contaminated. 



The insolated bouillon was then kept in 

 diffuse daylight for forty days and again 

 inoculated with the typhoid bacillus. Within 

 twenty-four hours the tubes of bouillon be- 

 tame turbid and plates made from them 

 showed innumerable colonies. 



It is diflacult to account for the effect of 

 insolation on culture media. Koux in his 



experiments on anthrax found that iusola* 

 tion of bouillon for tivo or three hours ren- 

 dered it unsuitable for germination of the- 

 spores, but if the bacilli were introduced 

 they would thrive. He attributes this alter- 

 ation to some chemical change which the 

 culture media undergo during the insolation. 

 He found also that if the insolated media 

 were kept in the dark or in diffuse daylight 

 for a time, the original nutritive qualities 

 were restored and germination of spores 

 would take place. Geisler and Janowski 

 observed the bactericidal j)roperties of inso- 

 lated media, but the latter coiUd find no 

 chemical alteration in such media. 



Percy Frankland in his chapter on action 

 of light on micro-oi'ganisms* concludes from 

 the results obtained by many investigators 

 ' that the effect is due to a process of oxi- 

 dation possibly brought about through the 

 agency of ozone or peroxide of hydrogen, or 

 both ; that all apparent^ dii-ect low tem- 

 perature oxidations require the presence of 

 water. And inasmuch as the bactericidal 

 action of light is unquestionably a case of 

 low temperature oxidation, there is the 

 strongest presumptive evidence, as well as 

 weighty experimental evidence, that moist- 

 ure, which practically means the possibility 

 of the presence of peroxide of hj^drogen or of 

 some similar material, is essential for its 

 manifestation. 't Westbrook (' Some of the 

 effects of sunlight on tetanus cultm-es. 

 Jour, of Pathol. & Bacteriol. III., Nov. 

 1894, 71 ') found that old broth cultures of 

 the tetanus bacillus in an atmosphere of 

 hydi-ogen were not in the least affected by 

 exposure to sunlight, either in regard to 

 their virulence or their rapiditj' of growth 

 on reinoculation. "When the same culture 

 was sealed up in the presence of au-, the 



*Micio-organisms in water, p. 390. 



fGelatine, to which were added different amounts 

 of the peroxide of hydrogen, was inoculated with the 

 bacillus typhi abdominalis and poured into plates. 

 Tliose plates in which more than one part of the 

 peroxide to 5000 of gelatine was used, were sterile. 



