24 BACTERIOLOGY. 



Temperativre. — The influence of temperature on bacteria will be 

 found to vary according to the species, but still for the majority we 

 may distinguish a maximum, optvmwm, and minimvm, temperature. 



Many grow best at the temperature of the blood, and hence the 

 value of nutrient agar-agar, which is not liquefied at 37° C. The 

 tubercle bacillus will only grow satisfactorily at a temperature 

 varying between 30° 0. and 41° 0. On the other hand, many forms 

 grow between the limits of 5° 0. and 45° 0. At these temperatures 

 their functional activity is paralysed, but they are not destroyed, 

 for by removal to favourable conditions they spring again into life. 

 Bacteria seem to have a special power of resisting the effects of cold. 

 It has been stated that comma-bacilli exposed to a temperature 

 of— 10° 0. for an hour, and bacilli of anthrax after exposure to a 

 temperature of —110° C, still retained their vitality. Temperatures 

 over 50° to 60° 0. destroy most bacteria, but not their spores ; spores 

 of anthrax retain their vitality after immersion in boiling water, but 

 are destroyed by prolonged boiling. Roughly speaking, all patho- 

 genic bacteria grow best at the temperature of the blood, and 

 non-pathogenic bacteria at the ordinary temperature of the room. 



Movement. — Bacteria probably grow best when left undisturbed. 

 Violent agitation of a vessel in which they are growing certainly 

 retards their growth, but a steady movement is stated not to affect 

 it ; at any rate, anthrax bacilli grow with enormous rapidity in the 

 blood-vessels, in spite of the circulation. 



Compressed Air. — Paul Bert maintained that a pressure of 

 twenty-three to twenty-four atmospheres stopped all development 

 of putrefactive bacteria. Oxygen, under a pressure of five or six 

 atmospheres, is stated to stop their growth. Other observers have, 

 however, obtained different restilts. 



Gases. — Hydrogen and carbonic acid are stated to stop the 

 movements of the motile bacteria. Chloroform is beUeved to arrest 

 the changes brought about by the zymogenic species. 



Electricity. — Oohn and Mendelssohn found that a constant 

 galvanic current produced a deleterious effect owing to electrolysis. 

 At the positive pole the hquid became distinctly acid, and at the 

 negative pole distinctly alkaline. With a weak current there 

 appeared to be no effect, two powerful cells at the very least being 

 necessary. 



Light. — Downes has shown that sunlight is fatal to putrefactive 

 bacteria. This is behoved to be due to a process of induced hyper- 

 oxidation, from which living organisms ordinarily are shielded by 

 protective developments of the cell-wall, or of colouring-matter, 



