1893.] 



Action of Light on Bacillus anthracis. 



35 



Theoretical. 



It remains to be seen whether any explanation can be given that 

 meets all the facts. The following suggestions seem fairly dedncible 

 so far. 



The spore is, in its fully ripe condition, a remarkably passive body, 

 and contains a smaller or larger store of reserve food materials, 

 generally of an oily or fatty nature. 



It is commonly conceded that the ripe spores of bacteria contain a 

 highly refringent substance like oil, and we know from the almost 

 universal occurrence of fat-like oils in the spores of Fungi and other 

 plants, including pollen grains, that such bodies constitute a very 

 common form of reserve material. ISTot only so, but the resistance of 

 spores to ordinary processes of staining and of sterilisation is intel- 

 ligible if they contain fatty substances. This, of course, does not 

 exclude the importance of the membrane and the other contents of a 

 spore in regard to its power of resistance. 



It appears at least possible that the bactericidal action of the 

 light is due to its destructive influence, in presence of oxygen, on the 

 fatty matters or other oxidisable substances forming the reserve 

 materials of the spore. Duclaux* has at any rate shown that 

 vegetable oils, such as olive and palm oils, are rapidly oxidised 

 if exposed to light, and, although we ought to be very careful in de- 

 ducing any explanation of physiological phenomena directly from 

 chemical experiments, we have here the significant fact that it is the 

 iays known to be so commonly concerned in promoting chemical 

 changes which are concerned in destroying the spores. The spores 

 are, in their passive resting state, to a certain extent comparable to a 

 flask of oil exposed to oxidation in the sunlight. Moreover, the 

 bacilli, which contain little or no fat, and the protoplasm of which is 

 far more accessible to the light, are found to resist the bactericidal 

 action of the light to a much greater extent than the spores. 



Of course, it may turn out that the action of the light is more pro- 

 found than the simple explanation offered assumes, and that the 

 physiological properties of the protoplasm are deeply concerned, but 

 I cannot help thinking that if this were the case we ought to obtain 

 more evidence of the action with the actively growing bacilli than 

 seems to be forthcoming from the results of the experiments. In any 

 case, it must be allowed that the solar action is direct on something 

 which is readily oxidisable in the spore : if the action were on the 

 protoplasm one would expect to find the vegetative bacilli succumb 

 more easily than the spores. 



* Duclaux, 'Ann. Inst. Pasteur,' vol. 1, 1887, p. 353. Duclaux says the oxidation 

 is the more rapid the more finely divided the oil is. See also Ballantyne, ' Journ, 

 Soc. Chem. Ind.,' 1891, p. 29, and Hartley, ' Journ. Soc. Arts,' 1893, p. 286. 



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