INFLUENCE OF TEMPERATURE. 77 



DIEUDONNE (I.) drew attention to the fact that, owing to the 

 possession by bacteria of a certain power of adaptation to climatic 

 conditions, no Jiard and fast lines can be drawn respecting the 

 limits of temperature within which growth is possible ; but that 

 by carefully controlling the stages of transition it is possible to 

 somewhat extend these limits. 



In ciliated bacteria spontaneous motion ceases when the tem- 

 perature of the environment approaches the lower or higher limit, 

 and they fall into a state of torpidity through cold or heat, from 

 which they recover as soon as the temperature once more becomes 

 favourable. 



Reference to the morphological influence of temperature has 

 already been made above (as also in 29), and will be exhaustively 

 described and illustrated, with a particularly fine example, in a 

 subsequent paragraph. The transforming and modifying power 

 of warmth also extends to other properties of bacteria; for example, 

 to the virulence of pathogenic bacteria, i.e. their capacity for 

 engendering disease. In the present work, however, not more 

 than a single one (on account of its general interest) can be re- 

 ferred to, viz., Pasteur's process of preventive inoculation for 

 anthrax. If Bacillus anthracis be cultivated in meat-broth for 

 twenty-four days at 42-^^ C., a virus (premier vaccin) is obtained 

 the virulence of which is so attenuated that sheep (the animal 

 most subject to anthrax) inoculated therewith experience only a 

 mild form of the complaint. If then inoculated with a second 

 culture prepared by exposure to the attenuating influence of a 

 temperature of 42-43 C. for only twelve days (second vaccin), 

 the animals no longer sicken, even if inoculated by unattenuated 

 B. anthracis, and are therefore immune against inoculative anthrax. 



62. Influence of Light. 



The old empirical hygiean maxim concerning the disease- 

 banishing power of the sun's rays which is well expressed by 

 the Italian proverb, "Where the sun does not enter the doctor 

 does" finds a full explanation in the bacteriological discovery 

 that the overwhelming majority of the fission fungi thrive much 

 better in darkness than in the light, and are, in fact, under certain 

 circumstances, killed by direct sunshine. This question of the 

 influence of light on bacteria has already formed the subject of 

 innumerable researches, most of which, however, are of purely 

 medical and hygienic interest, on which account their considera- 

 tion here must be restricted to a mere recapitulation of the main 

 points involved. A summary review of the literature of the 

 subject up to 1889 will be found in a work by J. RAUM (I.), which 

 in this particular is to some extent supplemented by the more 

 recent publications of TH. JANOWSKI (II.) and TH. GEISLER (I.). 



Most of our knowledge of the question was obtained from the 



