60 THE BACTERIA UNDER PHYSICAL AGENCIES 



Ludwigi and Bacillus Ilidzensis capsiilatus, the former developing only when the 

 temperature rose above 50 C., and the second producing endospores able to 

 withstand four hours' exposm-e in water at 100 C. without succumbing. 



DIEUDONNK (I.) drew attention to the fact that, owing to the possession by 

 bacteria of a certain power of adaptation to climatic conditions, no hard 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 temperature 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 en- 

 gendering disease. In the present work, however, not more than a single one 

 (on account of its general interest) can be referred to, viz., Pasteur's process of 

 preventive inoculation for anthrax. If Bacillus anthracis be cultivated in 

 meat-broth for twenty-four days at 42-43 C., a virus (premier vacciri) 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-^ 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 consideration 

 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 earliest 

 investigations therein, published in 1877 and 1878 by DOWNES and BLUNT (I. and 

 II.), who found that the growth of the bacteria is restricted by the influence of 

 diffuse white daylight and is completely stopped by sunshine. The blue and 

 violet rays proved the most injurious, the red and orange rays being weaker in 

 their action. The authors explained the injurious effect of light as an indirect 

 one, in that it strengthens the decomposing power of oxygen, the result being 

 the decomposition and destruction of the bacterial plasma. JAMIESON (I.), in 

 1882, gave another explanation of the phenomenon by attributing the injury 

 observed to the increase of temperature affected in the cells by the sun's rays. 

 The fallacy of this hypothesis which had been rejected by DOWNES (I.) was 

 demonstrated in 1885 by DUCLAUX (IV.), who was also the first to employ pure 



