THE MICROBIOLOGY OF THE ATMOSPHERE 



his Opportunities for carrying exotic microbes are greatest. The major 

 portion of the load carried across international boundaries by the world's 

 highly organized transport system consists of unprocessed plant material. 

 There are two dangers to be guarded against in this connection. An 

 important crop disease may be excluded from a country where the patho- 

 gen does not occur by: (i) prohibiting imports of possible host plants; 

 (2) inspection in the country of origin or on arrival; and (3) disinfection 

 (supplemented by local eradication measures should the pathogen gain a 

 temporary hold). The more insidious danger, however, is in an organism 

 which has settled do^\■n in its original home as an insignificant parasite 

 on a host with which it is in balanced relationship, suddenly being trans- 

 ported to a new country and finding a highly susceptible host-crop where 

 it can cause devastating losses — e.g. Puccinia polysora on African maize 

 (cf. p. 189), and Endothia parasitica^ a trivial parasite on oriental chestnuts, 

 but devastating when introduced into the United States of America from 

 Asia (McCubbin, 1944^, 1954). 



MEDICAL MYCOLOGY AND ALLERGY 



The winds, which had been suspected from antiquity of bearing 

 epidemic diseases, have been gradually exonerated so far as the major 

 human and animal epidemics are concerned. Malaria and yellow fever 

 come through the air, but only by the activity of their insect vectors. The 

 old scourges of cities are now known to be spread by vectors, water, milk, 

 or contact, and are no longer attributed to the winds. Air is not entirely 

 blameless, however. Droplets expelled from the mouth and nose spread 

 disease in confined places; wind carries pollens and other allergens; and 

 some of the less well-known fungus diseases of man, such as coccidioido- 

 mycosis and histoplasmosis, are clearly airborne (Rooks, 1954; Hoggan 

 et al. 1956; Furcolow & Horr, 1956; and Fiese, 1958). Air emerges as one 

 of the major routes for transport of micro-organisms, pollens, and many 

 crop pathogens. 



Outdoor airborne allergens appear to originate from vegetation above 

 ground, but not significantly from the soil (though the allergenic possi- 

 bilities of various soils themselves would be well worth testing). To a large 

 extent, therefore, their origin is an agricultural problem, aggravated by 

 our need to cultivate plants in pure stands. Fortunately, the interests 

 of farmers and allergic patients are to some extent identical. The farmer, 

 unless he is a seed grower, does not require his grass to scatter protein- 

 rich pollens uselessly, and the development of non-flowering strains of 

 grasses (from seed raised in other countries where conditions such as 

 length of day permit flowering) is beginning to attract the attention of 

 farmers and seed-merchants alike (Peterson et al.^ 1958); nor does the 

 farmer want his wheat-straw weakened by Alternaria or Cladosporium. 



Improved methods of measuring the spore concentrations of the air 

 are enabling us to bring many organisms forward for test as potential 



200 



