330 



NA TURE 



\_Feb. 26, 1874 



be heard all along the coast the sound of the Baroem, 

 a great wooden gong, announcing to the islanders the 

 departure of the "man-in-the-moon," who had taken 

 up his abode for more than a year amongst them. 



John C. Galton 



MICROSCOPIC EXAMINATIONS OF AIR 



A WORK* of the greatest importance on the above 

 subject has just been published in Calcutta by 

 Mr. Douglas Cunningham. The conclusions which he 

 has reached as the result of the experiment are so valu- 

 able that we deem it right to give them as great publicity 

 as possible. The following is Mr. Cunningham's de- 

 scription of the aeroscope with which he made his experi- 

 ments : — 



The apparatus employed in obtaining specimens was 

 a slightly modified form of that devised by Dr. Maddox. 

 It consisted of three thin brass tubes, two of which 

 slipped over the third central one and came into contact 

 with the opposite side of a projecting rim on its circum- 

 ference. This rim was formed by the margin of its dia- 

 phragm which divided the centre tube into two chambers. 

 It was of sufficient thickness to allow of a spindle passing 

 up through it. The latter terminated in a pointed 

 extremity, which came in contact with the upper end of 

 the bearing, and provided for the free rotation of the 

 system of tubes. Round the margin of the diaphragm 

 there was a set of perforations, to allow of the passage of 

 air through it, and, on the centre of its anterior surtace, 

 there was a square plate of glass with a slightly pro- 

 jecting rim on its lower margin. The anterior of the 

 two lateral tubes was provided with an expanded orifice, 

 and contained a small, finely-pointed funnel in its interior ; 

 the pointed extremity opening immediately in front of the 

 centre of the diaphragm-plate. The posterior tube was 

 quite simple, and had a good-sized fish-tail vane fitted 

 into a slit in its extremity. 



The following are Mr. Cunningham's conclusions : — 

 The most important conclusions to be derived from all 

 the preceding experiments regarding the dust contained 

 in the atmosphere in the vicinity of Calcutta appear to be 

 the following ; — 



1. The aeroscope affords a very convenient method for 

 obtaining specimens really representing the nature of the 

 true atmo.spheric dust. 



2. Specimens of dust washed from exposed surfaces 

 cannot be regarded as fair indices of the constituents 

 of atmospheric dust, since they are liable to contain 

 bodies which may have reached the surface otherwise 

 than by means of the air, as well as others which are the 

 result of local development. 



3. Specimens collected by gravitation also fail to indi 

 cate the nature and amount of organic cells contained in 

 the atmosphere, as the heavier amorphous and inorganic 

 constituents of the dust are deposited in relative excess 

 due to the method of collection. 



4. Dew also fails to afford a good means of investi- 

 gating the subject, as it is impossible to secure that all the 

 bodies really present in a specimen of it should be 

 collected into a sufficiently small space, and, moreover, 

 because it is liable to accidental contaminations, and also 

 affords a medium in which rapid growth and deve- 

 lopment are likely to take place. 



5. Distinct infusorial animalcules, their germs or ova, 

 are almost entirely absent from atmospheric dust and 

 even from many specimens of dust collected from exposed 

 surfaces. 



6. The cercomonads and amoeba; appearing in certain 

 specimens of pure rain-water appear to be zoospores de- 

 veloped from the mycelial filaments arising from common 

 atmospheric, spores. 



Microscopic Examinations of Air," by D. Douglas Cmmingliarn, W.Ii. 

 Surgeon H. M. Indian Medical Service (Calcutt.i). 



7. Distinct bacteria can hardly ever be detected among 

 the constituents of atmospheric dust, but fine molecules 

 of uncertain nature are almost always present in abun- 

 dance ; they frequently appear in specimens of rain-water 

 collected with all precautions to secure purity, and appear 

 in many cases to arise from the mycelium developed from 

 atmospheric spores. 



8. Distinct bacteria are frequently to be found amongst 

 the particles deposited from the moist air of sewers, 

 thougli almost entirely absent as constituents of common 

 atmospheric dust. 



9. The addition of dry dust, which has been exposed to 

 tropical heat, to putrescible fluids is followed by a rapid 

 development of fungi and bacteria, although recognisable 

 specimens of the latter are very rarely to be found in it 

 while dry. 



10. Spores and other vegetable cells are constantly 

 present in atmospheric dust, and usually occur in 

 considerable numbers : the majority of them are living 

 and capable of growth and development ; the amount 

 of them present in the air appears to be independent of 

 conditions of velocity and direction of wind ; and their 

 numbers are not diminished by moisture. 



11. No connection can be traced between the numbers 

 of bacteria, spores, &c., present in the air .ind the occur- 

 rence of diarrhcea, dysentery, cholera, ague, or dengue ; nor 

 between the presence or abundance of any special form 

 or forms of cells, and the prevalence of any of these 

 diseases. 



12. The amount of inorganic and amorphous particles 

 and other debris suspended in the atmosphere is directly 

 dependent on conditions of moisture and of velocity of 

 wind. 



If these results be compared with those obtained by 

 other observers, and detailed in the first section of this 

 report, it will be seen that they agree very closely with 

 those of M. Robin, only differing from them in indicating 

 the presence of a somewhat larger number of spores than 

 appeared in his observations. They differ almost equally 

 from those arrived at by Pouchet and Ehrcnberg. It is 

 somewhat difficult to understand how the former observer 

 so constantly failed to detect the presence of spores in his 

 experiments, but there is an apparent reason for Ehren- 

 berg's observation of the predominance of animal forms 

 in the atmosphere. His conclusions appear to have been 

 almost entirely founded on the results of the examination 

 of specimens of dust not directly obtained from the air, 

 but from surfaces on which it had been previously de- 

 posited from the air, such as leaves, tufts of moss, &c. 

 Now, as has already been indicated, it is certainly quite 

 unwarrantable to assume that all organisms found in such 

 specimens existed as such in the air, or were even derived 

 from the air in any way. All such surfaces are more or 

 less liable to contact-inoculation ; leaves and moss, for 

 example, are liable to this through the agency of insects 

 or birds. Moreover, with regard to many of the organisms 

 detected in such situations, it must be recollected that 

 there is no reason why they should not have arrived 

 there by means of active progression over the surface. 

 When surfaces are wet with rain, there is no reason why 

 Tardigrades, Rotifers, Anguiliuku, and many infusoria 

 should not travel o\er them from one point to another. 

 The journey accomplished at any one time may be small, 

 and its progress soon arrested by defective moisture; but, 

 unless they are deprived of vitality in the interval by 

 desiccation, they are ready for a fresh start when favour- 

 able conditions are again presented to them. 



It is hardly safe to venture on the vexed questions 

 regarding the origin of bacteria, but it may, at all events, 

 be stated that the results of the present experiments are 

 certainly not opposed to the belief in the transmission of 

 these organisms in some way or other by means of the 

 atmosphere ; for they were actually obsened among the 

 particles in moist air, the addition of dry dust to putre- 



