THE DESTRUCTION OF BACTERIA 63 



is accomplished, and the temperature at which the process takes place. 

 Microorganisips like the gonococcus and the Pfeiffer bacillus, are 

 destroyed by drying within a few hours. The cholera vibrio dried upon a 

 coverslip was found by Koch ' to be killed within four hours; by Burck- 

 holtz,^ 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 investiga- 

 tion, 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 tubercle 

 bacillus within two hours or less, the time depending upon the thick- 

 ness of the exposed layers and the material surrounding the bacilli. 

 Confirmatory researches have been published by Mignesco * and others. 

 The powerful disinfecting influence of sunlight upon bacteria suspended 

 in water has been shown by Buchner.' Observations in regard to the 

 influence of sunlight upon anthrax spores have been made by Arloing," 

 and similar observations upon a number 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 destruction, agree in finding definite and pow- 

 erful bactericidal action of sunlight. Diffuse light, of course, is less 

 active than direct sunlight. According to Buchner, typhoid bacilli are 

 inhibited by direct sunhght in one and one-half hours, by diffuse light 

 in five hours. A remarkable statement is made by Arloing, who claims 

 to have found that anthrax spores are more quickly destroyed by 

 direct sunlight than are the vegetative cells. This fact would call for 

 further confirmation. 



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



2 BwkhoUz, Arb. a. d. kais. Gesundheitsamt, v, 1889. 



» Koch, X Intemat. Med. Congress, Berlin, 1890. 



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



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



6 Arlmng, Compt. rend, de I'aead. d. sci., c, 1885. 



