450 PATHOGENIC MICROORGANISMS 



and others have shown that pneumococci slowly dried in sputum may 

 remain alive and virulent for 1 to 4 months, when protected from 

 light ; and as long as nineteen days when exposed to diffused light at 

 room temperature. Experiments hy Ottolenghi 39 have confirmed these 

 results; the virulence seems, in Ottolenghi 's experiments, to have 

 become considerably attenuated before death of the cocci. Recent 

 studies by Wood, 40 whose attention was focused chiefly upon pneumo- 

 coccus viability in finely divided sputum in a condition in which 

 inhalation transmission would be possible have shown that pneumo- 

 cocci survive for only about one and one-half hours, under ordinary 

 conditions of light and temperature. Exposed to strong sunlight, 

 pneumococci die off within an hour. 



Low temperatures slightly above zero are conducive to the pro- 

 longation of life and the preservation of virulence. 



The resistance of the pneumococcus to heat is low, 52 C. destroy- 

 ing it in ten minutes. 41 To germicidal agents, carbolic acid, bichlorid 

 of mercury, permanganate of potassium, etc., the pneumococcus is 

 sensitive, being destroyed by weak solutions after short exposures. 



The disinfection of sputum, difficult because of the protective coat- 

 ing of the secretions about the bacteria, has been recently studied by 

 Wadsworth. 42 The conclusions reached by this writer indicate that 

 pneumococci in exudates are most rapidly destroyed by twenty per 

 cent alcohol, other and stronger disinfectants being less efficient, prob- 

 ably because of slighter powers of diffusion. 



Differentiation of Pneumococcus from Streptococcus. Pneumo- 

 cocci and streptococci which do not differ in morphology from their 

 classic types can usually be differentiated from each other and identi- 

 fied by their morphological characters without difficulty; but it is 

 equally true that certain cultures of these organisms, either at the time 

 of their isolation or after cultivation on artificial media, approach the 

 type of the other so closely that it may be impossible to identify them 

 by their morphology alone. When such morphological variations occur 

 there are no constant cultural or pathogenic characters as yet demon- 

 strated which distinguish between these organisms. 



This lack of distinct cultural differences between pneumococci and 

 streptococci has not infrequently led to confusion, and that uncer- 



39 Ottolenghi, Cent, f . Bakt., xxv, 1889. 



40 Wood, Jour. Exp. Med., vii, 1905. 

 "Sternberg, Cent. f. Bakt., xii, 1891. 



42 Wadsworth, Jour. Inf. Diseases, iii, 1906. 



