Aug. 19, 1922 ] SECTION OF MICROBIOLOGY. [ M.IrJlf JoTn.. 



Sixth Fact: Experience shows that bacteria attacked by bacteriophage do 

 not remain passive; they defend themselves and are even capable, under certain 

 conditions, of acqtdring an immunity towards the parasite. 



This defence of the bacteria manifests itself by a double mechanism: the 

 bacteria surround themselves with a capsule, and secrete "aggressines" capable 

 of paralysing the lytic enzymes of the bacteriophage. Only the hypothesis of 

 bacteriophage being a parasite of bacteria conforms with these facts. 



Seventh Fact: The behaviour of bacteriophage towards physical and 

 chemical reagents is that of a living being, and does not agree with that of 

 an enzyme. 



The resistance of bacteriophage to the action of physical and chemical 

 reagents is intermediate between that of the vegetative and the spore forms of 

 ordinary bacteria. The resistance is less than that of certain ultramicrobes, 

 notably that of the tobacco mosaic. It is destroyed at 74°-75°C., but ceases 

 to develop at 43°. Between 43° and 74° it possesses no lytic action. As to 

 the action of the antiseptics, the bacteriophage is killed after twenty-four 

 hours' contact with a 1 per cent, solution of a neutral salt of quinine, after 

 forty-eight hours' contact with 95 per cent, alcohol, and by eight days' contact 

 with glycerin. The last-named liquid is precisely the medium employed for 

 preserving indefinitely an enzyme in soluble form. 



Eighth Fact: It is possible to extract the lytic enzymes free from the living 

 bacteriophage mirco-organism. 



If to one part of a culture of bacteriophage is added nine parts of absolute 

 alcohol and the mixture left forty-eight hours in contact, a precipitate is 

 obtained which contains bacteriolytic enzymes, while the bacteriophagic germs 

 are killed, which is proved by the failure of transmissibility in series of the 

 phenomenon. One can only understand this fact on the supposition of an 

 ultramicroscopic microbial parasite: the bacteria are dissolved by enzymes 

 secreted by the living ultramicroscopic germs, hence the action in series. In 

 the above experiment the ultramicroscopic germs are killed, while the enzymes 

 already secreted are preserved intact; hence only a lytic action is obtained 

 which is not transmissible in series. 



Ninth Fact: Bacteriophage is capable of adaptation. 



The bacteriophage is very sensitive to the action of acids— much more 

 sensitive than ordinary microbes. It can be accustomed progressively to live 

 in media containing quantities of an acid which would have been destructive 

 beforehand. The same fact is observed with glycerin. Adaptation is a preroga- 

 tive of living things. 



Tenth Fact: The properties of bacteriophage are essentially variable. 



It is impossible to isolate two strains of bacteriophage which are absolutely 

 identical as to their range of action on diflFerent bacterial species, and as to 

 their intensity of action towards each of these bacterial species. For a given 



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