84 



MICRO-OROrANISMS FROM THE BRISBANE AIR, 



The question now arises, How far do these distinct strains 

 of organisms represent distinct species ? 



Their individual differences are for the most part constant ; 

 that is to say, they breed true. I have cultivated most of the 

 forms through a succession of generations during twelve months, 

 and find them still true in minute detail to my original 

 descriptions. But it is important to note that one of their 

 characteristics, development of pigment, is much affected by 

 temperature. To test this point I have made simultaneous 

 agar cultures of all the coloured forms, growing one tube of 

 each in the incubator at 36deg. to 38deg. C, and another at 

 the temperature of the room, which at the time of the 

 experiment varied from 16 deg. to 22 deg. C. In six cases the 

 result was identical. The higher temperature stimulated the 

 early growth, which was more rapid, sometimes much more 

 rapid in the incubated tube during the first forty-eight hours, 

 but the growth remained whitish and never developed the 

 characteristic coloration. This was true of coccus y, C> /*. and ^, 

 andsbacillus a and ft. During the hot summer months these 

 bacteria lost their power of producing pigment, to regain it again 

 the next winter ; all except coccus {, in which the vivid orange 

 growth was never regained. It now develops only a pale orange. 

 On the other hand, in four cases the coloration was equally well, or 

 even slightly better developed in the incubated culture. This held 

 good of coccus >/ and A, and bacillus 8 and k. All these were 

 yellow growths. On the other hand, bacillus ft, which has a 

 yellow growth, was decolorised in the incubator, as were all 

 those which had a pink or orange growth. 



We see, therefore, that one of the most prominent 

 distinctions between our varieties varies with the temperature. 

 This does not impair its value as a real distinction ; but the 

 fact that in one form — coccus ( — the power of colour formation 

 has diminished, irrespective of temperature, certainly is of 

 significance. But when we take a general view of the differences 

 between the various forms, we find that some are as distinct as — 

 for example — roses from brambles ; while others present but minor 

 dift'erences, with a close general resemblance, like* the various kinds 

 of roses and brambles respectively, as to whose specific value no 

 two botanists are in agreement. For instance, the distinction 



