Dis'nniu'nox i\ nature 



41 



tiiu't typ(>s were recognized, l)('l()ii,ii;iiii;' lo the 

 j>;('iiiM';i ThcnntKuiindniiircs and M icroniono- 

 spora. 



Tliat the intestinal canal is the source of 

 thermophilic actinoniycetes was demon- 

 strateil by TsikHnsky and ]-iruini. 'I'he oc- 

 currence of thermophilic forms in soil has 

 fienerally been correlated witii the ai)plica- 

 tion of stable manures (Alishustin). Ilenssen 

 recently recorded the isolation from manures 

 and composts of 1 1 thermophilic species of 

 actinomycctcs placed in fi\'e <i;en(M'a, as 

 shown hi detail in Chapter 28, \'()1. II. 



Sewage is frequently found to contain ac- 

 tinoniycetes. As pointed out previously, 

 Kedzior was the first to demonstrate the 

 presence of thermophilic actinoniycetes in 

 sewage. Brussoff isolated an organism, desig- 

 nated as A. cloacae, definitely a strepto- 

 myces, from the slime of the Aachen purifi- 

 cation system. This organism was found 

 capalile of decomposing cellulose. Brussoff 

 accepted Beijerinck's and Krainsky's con- 

 cepts of the omnivorous nature of the actino- 

 niycetes. Still he believed that his organism 

 was capable of fixing nitrogen, a fact not 

 usually accepted at present, although it grew 

 better on nitrogen-containing media. 



Occurrence of Actinoniycetes in the At- 

 mosphere 



Actinoniycetes occur abundantly in the 

 atmosphere, both in the form of mycelium 

 and as spores. This can easily be illustrated 

 by exposing agar or gelatin plates to the air 

 for a few minutes or by collecting some of 

 the du.st and analyzing it. Actinoniycetes 

 are also unix'ersaily found on rocks, plants, 

 animals, clothing, food, and other surfaces 

 exposed to the atmosphere. Because of the 

 ability of actinoniycetes to withstand desic- 

 cation, their presence on such surfaces re- 

 sults from the breaking up of fine soil par- 

 ticles suspended in the atmosphere and the 

 drying of water drops. \\'iii(l currents are 



also largely I'esponsible for I heir wide dislri- 

 but ion. 



The presence of microscopic; particles of 

 dust in the air was known to the ancients. 

 The Roman poet I.ucretius first observed 

 such particles by passing a ray of sunlight 

 through a darkened room. With the birth of 

 modern microbiology, ever-gi'owing atten- 

 tion was paid to the microbes found in the 

 dust. Leeuwenhoek observed them in rain 

 drops; Ehrenburg found them in rain water 

 and in snow; J. Tyndall saw them directly 

 in the dust. The whole (juestion of sponta- 

 neous generation, which aroused so much 

 attention and which was settled largely 

 through the work of Pasteur, had a great 

 deal to do with the interest in the microbial 

 population of the atmosphere. The question 

 of contagion and the problems of epidemics 

 appeared to be at that time closely related 

 to the air as a carrier of microbial agents. 

 More recently, the bearing of the dust micro- 

 flora upon the problem of allergy has begun 

 to receive considerable attention. 



Foulertoii and I'rice-Jones spoke of the 

 isolation of actinoniycetes (Sfrcptothrix crijth- 

 rea) as air contaminants. Tli(\v also men- 

 tioned the isolation of actinomycete cultures 

 (»S/. leucea and .S7. leucen saprophijiica) from 

 sewage and from drinking water. 



Lidwell suggested that the problem of 

 sampling air for microlies comprises collec- 

 tion ()f the sample from the atmosphere and 

 the determination of the microbial cells in 

 the sample, their enumeration, and their 

 classification. Methods of air sampHng in- 

 clude: (a) sedimentation, usually into open 

 dishes; (b) filtration, through wool, sand, or 

 other materials; (c) cent I'ifugat ion; (d) col- 

 lection in li(iui(l by bubbling air through it; 

 (e) electrostatic pi'eci])itation. 



Special apparatus was constructed for col- 

 lecting atmospheric dust. I']xp()sures were 

 made at different altitudes and under dif- 

 ferent conditions. The first comprehensive 

 studv was undei-takeii 1)V Miciuel in 1883. 



