PRODUCTS OF BACTERIAL ACTIVITY. 31 



Temperature : It is impossible to establish an exact average 

 temperature limit. As a rule bacteria will not develop in 

 a temperature lower than 10 C., or higher than 40 C. 

 Exceptional germs will grow very feebly, or possibly only 

 retain their vitality, in a temperature as low as 6 C. and as 

 high as 70 C. A temperature of 10 C. will inhibit the 

 growth of many bacteria, but will not kill them. Some 

 germs safely withstand freezing. Ravenel exposed anthrax 

 spores, diphtheria and typhoid bacilli, and Bacillus prodigiosus 

 to liquid air ( 312 F.) for from three hours to thirty min- 

 utes, and when the spores and germs were transplanted to 

 bouillon they grew with their customary rapidity. A tem- 

 perature over 60 to 70 C. is fatal to most bacteria. Spores 

 are more resistant, but are killed in boiling water in a few 

 minutes. They will withstand dry heat (150 C.) for hours. 

 The non-pathogenic bacteria are better able to accommodate 

 themselves to temperature extremes than the pathogenic 

 germs, all of which develop best at the body temperature. 



Association : The influence of one species of bacteria upon 

 the growth of another, when associated with it in culture, is a 

 matter of considerable interest as well as importance. Such 

 association will at times increase or diminish the virulence 

 of pathogenic germs. The toxin of the streptococcus is much 

 more virulent when obtained from a combined culture of 

 Streptococcus pyogenes and Bacillus prodigiosus. On the other 

 hand, the virulence of anthrax is diminished when the germ is 

 associated in culture with the Bacillus prodigiosus. Sana- 

 relli's bacillus of yellow fever grows better when associated 

 with certain moulds. 



Products of bacterial activity: In both the animal 

 and the vegetable world the result of metabolism is certain 

 waste products and substances which are necessary to support 

 life. Some of these waste products are highly injurious. 

 The products of bacterial activity are many, some of them 

 inert, and others more or less toxic. 



Pigment : Those bacteria which produce pigment are said 

 to be chromogenic. The pigment may be of any shade. The 

 most beautiful colors are produced, and attempts are now 

 being made to utilize these pigments commercially. These 



