^oSmai,Erim'] Atmospheric Particles. 287 



by any form of aspirator, or by shaking together frequently ad- 

 mitted volumes of air and distilled water ; for this reason, that before 

 you have proof of having entrapped any living molecules, admitting 

 the purity of the water, you have to allow deposition, decant and 

 examine the deposit by droplets under a high power, at least an 

 -eighth objective, and are even then, under the most careful scrutiny, 

 by no means certain that very many of the hghtest and minutest 

 have not been either pom-ed away or passed unnoticed. 



A most delicate scum is sometimes seen on the water prior to 

 decanting the mass ; but this, so far as I am aware, has been entirely 

 overlooked, and only the deposit exaroined ; yet such scum has afforded 

 different objects to those in the sediment. I am not in any way 

 alluding to artificial infusions of vegetable, animal, or mineral matter 

 in water ; in the two former, the scum is too evident to escape ob- 

 servation. Nor does it follow, if the minutest germs be living, that 

 they should subside at all ; they may move through various depths 

 unrecognized. The j)lan I propose is to try and entrap these atmo- 

 spheric motes into a small compass, and under ordinary conditions 

 of the external air ; then, without allowing more than a few hours 

 to elapse, proceed to their examination; for this reason: — Suppose 

 an apparatus, where the air is drawn for weeks over or through the 

 same water, and let us fui'ther suppose numerous germs were ob- 

 tained, and a due calculation made of even the quantity of air drawn 

 through hourly, it by no means follows that all those germs were 

 drawn direct from the atmosphere, for those which have their habitat 

 in water or damp places may have germinated and divided many 

 times ere the experiment is finished, such subdivision or repetition 

 giving false conclusions ; and, moreover, many may have perished 

 under the conditions employed to detect them. 



If, then, we can draw these particles into a small space, the next 

 object would be to try and make them pass through at least some 

 of their phases of life, under careful watching with the microscope. 

 Even supposing we have entrapped and developed some of the 

 germs, we shall not have established their relation to disease ; to do 

 this would require a very numerous and careful course of observa- 

 tions; but one thing we shall have done, and that is have deter- 

 mined, at least partially, most of the largest of these germs be not 

 those of the commonest forms of mildew, and such as we meet with 

 continually in our food, and which most probably have not the 

 ^slightest relation to disease, and the minutest, those which are 

 ranged among the monads, bacteria, and vibrios. 



To assist in this inquiry I have made the following apparatus as 

 a hollow wind vane, but which can be used in various ways, and 

 by which I hope to obtain results bearing on this important ques- 

 tion, which as yet cannot be admitted as settled. 



On reference to Fig. 1 (Plate LIV.) it will be seen as in use as 



