42 BACTERIOLOGY. 



is not interfered with by either the presence or absence 

 of free oxygen, yet experiments demonstrate that the 

 products of their growth are different under the varying 

 conditions of absence or presence of this gas. For ex- 

 ample : in the case of certain of the chromogenic forms 

 the presence or absence of oxygen has a very decided 

 effect upon the production of the pigments by which 

 they are characterized. 



Note. — Observe the difference between the intensity 

 of color produced upon the surface of the medium and 

 that along the track of the needle in stab-cultures of 

 bacillus prodigiosus and of spirillum rubrum. In the 

 former the red color is apparently a product dependent 

 upon the presence of oxygen, while in the latter the 

 greatest intensity of color occurs at the point furthest 

 removed from the action of oxygen. 



Another factor which plays a highly important part 

 in the biological functions of these organisms is the 

 temperature under which they exist. The extremes of 

 temperature between which the majority of bacteria are 

 known to grow range from 5.5° to 43° C. At the 

 former temperature development is hardly appreciable ; 

 it becomes more and more active until 38° C. is reached, 

 when it is at its optimum, and, as a rule, ceases at 

 43^^ C. ; though species exist that multiply at as high 

 a temperature as 70° C. and others at as low as 0° C. 

 The investigations of Globig,^ Miquel,^ and Macfadyen 

 and BloxalP have revealed the existence in the soil, 



1 Globig : Zeitschrift fiir Hygiene, Bd. iii. S. 294. 



'' Miquel : Annales de Micrographie, 1888, pp. 4 to 10. 



3 Macfadyen and Bloxall : Journal of Patli. and Bact., vol. iii. part i, 



