THE MICROBIOLOGY OF THE ATMOSPHERE 



Although most spores are deposited near their source, some are 

 readily transported to great distances. Transport over long distances 

 plays a regular role in some crop disease epidemics, and presumably in 

 the movement of many other organisms. Mountain ranges, oceans, and 

 deserts, may all be effective barriers to dispersal. Although conditions in 

 the upper air, especially in cloud, may not be unfavourable for survival, 

 loss of viability rather than failure of the transport mechanism limits the 

 colonization range of many organisms. Enhanced variability may be 

 expected among microbes that survive exposure to ultra-violet radiation. 

 Because of the overwhelming importance of unsuspected near-by 

 sources, it is often difficult to be sure that an organism observed has come 

 from a great distance. 



Implications of Aerobiology 



BIOLOGICAL warfare 



It seems that microbiological weapons have not been used on any large 

 scale by man against man. The example of myxomatosis in rabbits should 

 convince sceptics of what might happen when all conditions are suitable 

 for epidemic spread. The topic is shrouded in official secrecy, but the 

 little information already released suggests that, if deliberate dissemination 

 of pathogens (or toxins) were ever attempted, contamination of the air 

 might be one of the dangers to be anticipated. Rosebury et al. (1947), 

 from their comprehensive analysis of the principles of bacterial warfare, 

 consider that the airborne group of pathogens contains the most important 

 infective agents for war use {see also Rosebury, 1947, 1949)- The published 

 studies on air-sampling equipment and epidemiology that come from 

 official defence laboratories are small compensation for this threat by man 

 to his own health and agriculture. 



ISOLATION, QUARANTINE, AND GEOGRAPHICAL DISTRIBUTION 



The prodigious reproductive powers of microbes always excites 

 comment and is particularly remarkable in the matter of the number of 

 spores produced by fungi. The wastage of spores must be enormous. 

 The w^orld is more or less fully populated with fungi and, within reason- 

 able geographic and climatic bounds, a fresh substratum will rapidly 

 select its normal flora from the ample supply of suitable spores brought 

 to it. In crop pathology we study a system that is temporarily unbalanced 

 by human activities — large, reasonably pure stands of susceptible, 'arti- 

 ficial' crop-plants which are renewed at regular intervals, are especially 

 subject to attacks by parasites. Dispersal gradients become obvious under 

 these conditions, and our isolation and quarantine methods can play a 

 major role in limiting the development of a fungus flora on a crop. 



Willis (1940) claims that 'nothing in the distribution of plants would 

 lead anyone to suppose that the "mechanisms for dispersal" have pro- 

 duced for the plants that possess them any wider dispersal than usual'. 



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