326 PATHOGENIC MICROORGANISMS 



Desiccation is usually well borne, staphylococci remaining alive for 

 six to fourteen weeks when dried upon paper or cloth.' On slant agar, 

 staphylococci may be safely left for three or four months without trans- 

 plantation, and remain alive.^ 



The resistance of staphylococci to chemicals, a question of great 

 surgical importance, has been made the subject of extensive researches, 

 notably by Liibbert,^ Abbott,'' Franzott,^ and many others. According 

 to Liibbert, inhibition of staphylococcus growth is attained by the use of 

 boric acid 1 in 327, salicylic acid 1 in 650, corrosive sublimate 1 in 

 80,000, carbolic acid 1 in 800, thymol 1 in 11,000. Staphylococci are 

 killed by corrosive sublimate 1 in 1,000 in ten minutes, by carbolic acid 

 1 per cent in 35 minutes, 3 per cent in 2 minutes (Franzott). Ethyl 

 alcohol," even when absolute, is not very efficient as a disinfectant. 

 Nascent iodin, as split off from iodoform in wounds, is extremely power- 

 ful in destroying staphylococci. 



Pathogenicity. — Separate strains of Staphylococcus pyogenes aureus 

 show wide variations in relative virulence. The most highly virulent 

 are usually those recently isolated from human suppurative lesions, 

 but no definite rule can be formulated in this respect. The virulence 

 of a given strain, furthermore, may be occasionally enhanced by re- 

 peated passages through the body of a susceptible animal. Prolonged 

 cultivation upon artificial media is liable to decrease the virulence of any 

 given strain, though this is not regularly the case. There are, more- 

 over, unquestionably, many staphylococci constantly present in the air, 

 dust, and water, which although morphologically and culturally not 

 unlike the pathogenically important species, may be regarded as 

 harmless saprophytes. 



The susceptibility of animals to staphylococcus infection is, 

 likewise, subject to extreme variations, depending both upon differ- 

 ences between species and upon fortuitous individual differences 

 in susceptibility among animals within the same species. Animals 

 on the whole are less susceptible to staphylococcus than is man. 

 Among the ordinary laboratory animals, rabbits are most sus- 

 ceptible to this microorganism. Mice, and especially the white 



1 Deslongchamps, Paris, 1897. 

 'Posset, Fort. d. Med., 2 and 3, 1885. 

 ^Liibbert, "Biol. Untersuch.," Wurzburg, 1886. 

 'Abbott, Medical News, Phila., 1886. 

 ^FranzoU, Zeit. f. Hyg., 1893. 

 ^Hanel, Beit. z. klin. Chir., xxvL 



