30 



BACTERIA. 



GROWTH AND REPRODUCTION depend upon the conditions of 

 temperature. There is a certain minimum, optimum and maxi- 

 mum for each species ; for instance (in degrees Centigrade) 



VIG. 23. Bacillus megaterium : a outline of a 

 living, vegetative cell-rod ; b a living, motile, pair of 

 rods ; p a similar 4-celled rod after the effects of 

 iodine alcohol ; c a 5-celled rod in the first stages of 

 spore-formation ; d-f successive stages of spore- 

 formation in one and the same pair of rods (in the 

 course of an afternoon) ; r a rod with mature spores ; 

 g'-;/ 3 three stages of a 5-celled rod, with spores sown 

 in nutritive solution ; Ji'-fi 3 , i,fe, I stages of germina- 

 tion ; m a rod in the act of transverse division, 

 grown out from a spore which had been sown eight 

 hours previously. (After de Bary ; a mag. 250, the 

 other figures 600 times). 



Bacillus subtilis 



B. anlhracis 



Spirillum cholerce asiaticce 



Bacterium tuberculosis 



Minim. 

 + 6 



15 



8 



Opt. 

 c. 30 

 20-25 

 37 



28 37-38 



FIG. 29. Bacillus amj/lobacter. 

 Motile rods, partly cylindrical 

 and without spores, partly 

 swollen into various special 

 shapes and wilh spore-forma- 

 tion in the swelling, s Mature 

 spore, with thick mucilaginous 

 envelope. (After de Bary ; 

 mag. 600 times, with the excep- 

 tion of s, which is more highly 

 magnified.) 



Maxim. 

 + 50 



43 



40 (but grows only 



feebly if under 



16). 

 42 



The functions of life cease on a slight excess of the maximum 

 or minimum temperature, numbness setting in when either of 

 these limits is passed. Crenothrix-ila.resLda provided with muci- 

 laginous envelopes may, according to Zopf, sustain a tempera- 

 ture of 10. Some Bacteria are said to be able to resist the 

 exposure to as low a temperature as 110 for a short time. It is 

 not known at what degree of cold the death of the Bacteria oc- 

 curs : the greatest degree of heat which the vegetative cells can 



