54 ACTIVITIES OF BACTERIA. 



with bacilli, an atmosphere containing oxygen is necessary 

 in order for injury to occur. According to Dieudonne, 

 anthrax spores upon agar plates were dead after an expo- 

 sure to direct sunlight for three and a half hours (bacilli 

 in one and a half hours) ; if oxygen was excluded, an ex- 

 posure of nine hours produced no injury. 



F. The Activities of Bacteria, 



Especially in Regard to the Application of the 

 Same to Diagnostic Purposes. 



The activities of bacteria in the test-tube may be des- 

 ignated 1 as: (1) mechanical, (2) optical, (3) thermal, 



(4) chemical. They will here be discussed in this order; 

 a fifth section will show how the activities of the bac- 

 teria enable them to become the causes of disease (patho- 

 genic action). 



All the activities of a given variety of bacterium are 

 especially dependent upon, (1) the momentary condition of 

 the bacterium; (2) the nutrient substratum; (3) the entrance 

 of air; (4) the temperature; (5) the illumination. 



Since we have already stated what is most important re- 

 garding the influence of temperature and light, in the 

 following ' I must especially discuss the influence of the 

 nutrient medium and the admission of air on one side, and 

 the composition of the final culture on the other. The latter 

 point must always be made especially prominent, in order 

 to show, in the largest possible range, how very much the 

 activity of bacteria changes, according as they are examined 

 when in a fall zymogenic, chromogenic, or pathogenic condition, 

 or in an attenuated state. 



J It is self-evident that to-day a division of bacteria into zymo- 

 genic, saprogenic, chromogenic, and pathogenic is not acceptable. 

 Bact. coli causes, for example, in sugar-solutions powerful fermenta- 

 tion ; on nutrient media rich in albumin it produces abundant indol 

 and sulphuretted hydrogen; it forms upon potato very often a rather 

 bright brownish-yellow colored layer, and is besides pathogenic for 

 animals and man; it therefore combines the properties of all four 

 groups. 



