70 



MICROSCOPIC EXAMINATIONS OF AIR* 



The report of Dr. Douglas Cunningham on examination of air 

 in India contains some im^^ortant results bearing on recent inquiry 

 and speculation. It commences with a digest of the literature of 

 atmospheric micrography from Ehrenberg to the present, and then 

 details the methods adopted in his own investigations. The 

 results are tabulated in connection with rainfall, velocity of wind, 

 and prevalent diseases. The amount of dust visible to the naked 

 eye varied extremely, in some cases being almost or entirely 

 inappreciable, in others present in considerable quantity, whilst iu 

 one or two cases in which dust storms had occurred during the 

 period of exposure the amount was so great as actually to form a 

 small heap opposite the orifice of the funnel, and to require the 

 addition of a considerable quantity of fresh glycerine ere contact 

 between the slide and cover could be secured. The relative pro- 

 portions of the various classes of microscopic constituents present 

 also varied, an increase in one of them being by no means 

 necessarily or invariably associated with an increase in others. For 

 example, dry, windy weather caused a great increase in the amount 

 of silicious, carbonaceous, and amorphous particles, and other 

 debris, but certainly did not cause a proportionate increase in the 

 number of spores and other fungal and algal cells. On the other 

 hand, the occurrence of moist weather Avas accompanied by a great 

 diminution in the quantity of the former without, in many cases, 

 appearing to influence the numbers of the latter at all, or in a 

 similar direction. Where a very large quantity of coarse and 

 amorphous matter is present, it is no doubt ofte'n difficult to determine 

 the absolute numbers of the spores, &c., in a preparation, but it is, 

 at all events, easy to see that the increase of them, if it exists, is 

 not proportional. The influence of moisture in diminishing the 

 numbers of the coarser atmospheric particles is evident from the 

 tables, but it does not appear to affect that of the spores, &c., in 

 the same manner, but, on the contrary, rather tends to increase it, 

 for it will be seen that the number of such bodies exceeded the 

 average in 17 instances during the moist period, and only an eight 

 during the dry one. Velocity of wind seems to exert as little 

 influence on the numbers of spores and similar cells in the atmos- 

 phere as moisture. A low velocity, in many instances, was 

 coincident with a high number of spores, and vice versa. 



Of the special elements appearing as constituents in these 

 preparations of atmospheric dust, it may be stated that those of 

 most constant occurrence were particles of silica, amorphous 

 granular masses, carbon, lime, starch corpuscles, cells, hairs, and 

 other fragments of vegetable tissues, fibres of cotton, hairs and 

 scales of insects, oil globules, pollen grains, spores and cells of 



* From the Ninth Annual Eeport of the Sanitary Commissioner with the 

 Government of India, Calcutta, 1872. 



