Aug. 19, 1922 ] SECTION OF MICROBIOLOGY. [MBlrc^XKNAL 



been built up slowly in accordance with the theories of evolution, then an 

 amoeba and a bacterium must be recognized as highly developed organisms in 

 comparison with much more primitive forms which once existed, and probably 

 still exist, in nature. It is quite possible that an ultramicroscopic virus belongs 

 somewhere in this vast field of life where the organization is lower than that 

 of the bacterium or amoeba. It may be living protoplasm that forms no 

 definite individuals, or an enzyme with power of growth. 



In the first instance attempts were made to demonstrate the presence of 

 non-pathogenic filter-passing viruses. As is well known, in the case of ordinary 

 bacteria, for every pathogenic micro-organism discovered many non-patho- 

 genic varieties of the same type have been found in nature, and it seems highly 

 probable that the same rule will be found to hold good in the case of ultra- 

 microscopic viruses. It is difficult, however, to obtain proof of their existence, 

 as pathogenicity is the only definite evidence we have at the present time of 

 the presence of an ultramicroscopic virus. On the other hand, it seems 

 probable that if non-pathogenic varieties exist in nature these should be more 

 easily cultivated than the pathogenic varieties. 



The first experiments were carried out with such materials as soil, dung, 

 grass, hay, straw, and with water from ponds. Cultivations were made on a 

 large number of special media and under special conditions. Experiments 

 were also carried out with pathological material obtained from distemper in 

 dogs, from vaccinia, and from various other sources. The first results of 

 interest were obtained with vaccinia. Inoculations were made on to ordinary 

 agar tubes, and on to tubes of special egg media such as I used in my experi- 

 ments for the cultivation of Johnes's bacillus and the lepra bacilli of man and 

 of rats. It will be impossible to describe all these in detail, but the essential 

 part of one series consists in the incorporation in the media of the dead bodies 

 of certain acid-fast bacilli such as Bacillus phlei, which proved to be so success- 

 ful in the cultivation of Johnes's bacillus. The egg media usually grew a 

 number of colonies of micrococci and diphtheroids, while the agar tubes grew 

 only a few colonies of micrococci. In the case of the egg media it was noted 

 that in a few days certain parts of the micrococcus growth sometimes became 

 dull, and in appearance rather resembled bacterial growth in which amoebae 

 were also growing. On the agar media the colonies of micrococci ocassionally 

 showed a translucent or transparent change, which started as more or less 

 clear spots at the margins of the colonies. It was also found that some of these 

 colonies could not be subcultured, but if kept the transparent change extended 

 over most of the colony. 



On examination of these glassy areas nothing but minute granules, staining 

 reddish with Giemsa, could be seen. Further experiments showed that if a 

 colony of the white micrococcus that had started to become transparent was 

 plated out instead of being subcultured as a streak, then the micrococcus grew 

 and a pure streak culture from certain of these colonies could be obtained. On 

 the other hand, if the plate cultures (made by inoculating the condensation 



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