28 THE VICTORIAN NATURALIST. 



No doubt this result is in part due to the length of time elapsing 

 before a bacteriological examination was undertaken. 



The majority of the micro-organisms growing in sample No. 2 

 consisted of a rapidly liquefying bacillus, which slowly produced 

 a green pigment {Bacillus Jluorcscens liqtiefaciens). This 

 organism is commonly found in fresh water. 



Sample i differed from 2 in containing considerable numbers 

 of white and green moulds {Oidium albicans and Penicilliinn 

 glaucum). There were also present a few members of the " Hay 

 bacillus" group, and a very limited number of Bacillus Jluorescens 

 lique/aciens, the pigment in this case being produced more 

 slowly than in sample 2. 



Each sample also contained a few members of the "colon" 

 group. 



Remarks. — It is characteristic of the common "air organisms " 

 that many of them produce varieties of red, pink, yellow, and 

 brown pigments. It is noteworthy that these pigment-producing 

 bacteria were entirely absent from the sample examined, and this 

 fact would seem to indicate that the atmospheric dust on the 

 occasions of the " red rain " phenomenon was not of the 

 character usually found. This abnormality was further indicated 

 by the presence of the colon group in each sample. Extensive 

 laboratory experiments have shown that the colon bacillus is 

 rarely found normally in the atmosphere. 



As to the origin of solid material in the samples, the bacterio- 

 logical results in the case of sample 2 would seem to indicate 

 that the locality had not been subjected to drought of a recent 

 date, owing to the numerous water bacteria present. Such, 

 however, does not appear to be so markedly the case in sample 

 I.— R. J. Bull, M.D. 



We had. however, no particular desire to endeavour to discover 

 what might be present in an " everyday " sample of Melbourne 

 dust, though that is by no means unimportant. Hence we 

 purposely waited until the whole of this had been swept away 

 in order that our sample might contain only material carried 

 from afar. It would, we think, be safe to say that none of 

 the material we are describing had been derived from an area 

 within 30 miles north or west of Melbourne. It would be 

 equally safe to affirm that much of it was derived from areas 

 ranging from that distance up to 300 or more miles north and 

 west. The Diatomace?e were most probably mainly carried from 

 the low-lying swamps and salt lakes which fringe the River 

 Murray and other waterways throughout northern and north- 

 western Victoria, and beyond the South Australian border. That 

 they live and grow in profusion under conditions such as are 

 known to obtain within the area in question is a matter of 

 observation. During abnormal seasons of drought, such as have 



