THE DESTRUCTION OF BACTERIA 77 



by the age of the culture investigated, the rapidity with which the 

 withdrawal of moisture is accomplished, and the temperature at 

 which the process takes place. Microorganisms like the gonococcus 

 and the Pfeiffcr bacillus are destroyed by drying within a few 

 hours. The cholera vibrio dried upon a coverslip was found by 

 Koch 2 to be killed within four hours; by Burkholtz, 3 to survive 

 about twenty-four hours. The spore-forms of bacteria are infinitely 

 more resistant to this influence than are the vegetative forms, though 

 they may be destroyed by rapid and complete drying in a desiccator. 



It is self-evident that many discrepancies in the experimental 

 results of various authors may depend upon the technique of inves- 

 tigation, since the degree of drying attained depends intimately upon 

 the thickness and consistence of the material investigated, and upon 

 the methods employed for desiccation. 



Light. Direct sunlight is a powerful germicide for all bacteria 

 except a limited number of species like the thio- or sulphur bacteria, 

 which utilize sunlight for their metabolic processes as do the green 

 plants. 



Koch* has shown that exposure to sunlight will destroy the tuber- 

 cle bacillus within two hours or less, the time depending upon the 

 thickness of the exposed layers and the material surrounding the 

 bacilli. Confirmatory researches have been published by Mignesco 5 

 and others. The powerful disinfecting influence of sunlight upon 

 bacteria suspended in water has been shown by Buchner. 6 Observa- 

 tions in regard to the influence of sunlight upon anthrax spores 

 have been made by Arloing, 7 and similar observations upon a num- 

 ber of other microorganisms have been carried out by Dieudonne, 

 Janowski, v. Esmarch, and many others. All these observers, while 

 differing somewhat as to the time necessary for bacterial destruc- 

 tion, agree in finding definite and powerful bactericidal action of 

 sunlight. Diffuse light, of course, is less active than direct sunlight. 

 According to Buchner, typhoid bacilli are inhibited by direct sun- 

 light in one and one-half hours, by diffuse light in five hours. A 

 remarkable statement is made by Arloing, who claims to have found 



2 Koch, Arb. a. d. kais. Gesundheitsamt, iii, 1887. 



3 Burkholtz, Arb. a. d. kais. Gesundheitsamt, v, 1889. 



4 Koch, X Internat. Med. Congress, Berlin, 1890. 

 8 Mignesco, Arch, f . Hyg., xxv, 1896. 

 'Buchner, Cent. f. Bakt., I, xi, 1892. 

 ''Arloing, Compt. rend, de 1'acad. d. sci., c. 1885. 



