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THAT the air we breathe is more or less laden with living organisms is a fact which is far from acceptable to most persons, and yet it would require but little persuasion to convince the majority of mankind that air without organisms would be undesirable indeed; for without one micro-organism at least, which is very widely distributed in the air, we should have to forego those numerous, complex, and much appreciated pleasures which are derived from the consumption of alcohol in its various forms. How many would vote the earth flat and stale but for the products which are alone elaborated by yeast, which was the first micro-organism to receive attention, and which, in spite of the many powerfully organised endeavours to undermine its position, is likely also to be the last to absorb the interest of man.

But there are other micro-organisms in the air besides yeast, and it is the firm conviction that many zymotic diseases are propagated by means of air-carried microbes, that renders the investigation of the subject of aërial micro-organisms peculiarly interesting and attractive.

The systematic examination of the aërial microbia commences with those marvellous discoveries with which the name of Pasteur is so inseparably connected, and with which the latter half of the nineteenth century will for ever be associated.

These now classical researches of Pasteur's on the presence of micro-organisms in the atmosphere were undertaken in connection with the fierce controversy which raged thirty years ago on the Spontaneous Generation of Life.

The supporters of this doctrine contended that the presence of the smallest particle of air was sufficient to determine the generation of low forms of life in certain highly putrescible substances, such as milk, blood, broth, and the like. But the opposition to this theory, marshalled by M. Pasteur, contended that it was not the air, but certain living germs suspended in the air, which, gaining access to


In the country, as might have been anticipated, I have found a very appreciably smaller number of micro-organisms than in air in London. Moreover, the more remote the place is from houses and from the frequented thoroughfares of traffic, the dust of which is always rich in refuse organic matter, the freer does the air become from suspended microbes. Thus the air of an extensive heath near Norwich was found to contain from five to seven micro-organisms in the two gallons of air, whilst in that of a garden near Norwich were found as many as thirty-one. Again, on the Chalk Downs in Surrey I found on one occasion only two; this, however, was very early in the year (February 1886), and snow was on the ground; later on, at the end of May in the same year, I found thirteen, but in a garden near Reigate on the same day there were twenty-five. So that there is a considerable difference found in the microbial richness of the air in different places in the country. I have also tested the London air under the most favourable conditions, viz.: in the open spaces in the parks, and these experiments show that although such air generally contains fewer microbes than the air even on the roof of the Science Schools (at a height of seventy feet), yet the number is in excess of that found in the country, although the situations chosen were large surfaces of grass from which little or no dust could be blown about. But the air in the streets was found to contain numbers immensely in excess of anything that was discovered in the country, the result being in some instances as high as 554 in the two gallons of air. This last figure was obtained in the Exhibition Road on a dry and dusty day when vast multitudes of people were thronging to the Colonial and Indian Exhibition which was then open.

The striking contrast to the number of micro-organisms found in the various places previously referred to is the number found in the air at sea. I have not myself had an opportunity of making any experiments at sea, but some have recently been made by Dr. Fischer, a surgeon in the German navy. From his experiments it would appear that the maximum distance to which, under ordinary circumstances, micro-organisms can be transported across the sea lies between 70 and 120 sea miles, and that beyond this distance they are almost invariably absent. A point of particular interest in connection with Dr. Fischer's experiments is that they show in a very striking manner that the microbes, which are always abundantly present in ordinary sea water, are not communicated to the air, excepting in the closest proximity to the surface, even when the ocean is much disturbed.

Before passing on to the microbial condition of the air within doors, I will just briefly refer to some experiments which I made at different altitudes, fully confirming those of Pasteur to which

reference has already been made. Two gallons of air examined on the top and at the bottom of Primrose Hill, gave respectively nine and twenty-four micro-organisms. Again, the same volume of air examined at Norwich Cathedral on the top of the spire (300 feet) gave seven, on the tower (180 feet) nine, whilst on the ground eighteen were found.

Again, at St. Paul's Cathedral, the Golden Gallery yielded eleven, the Stone Gallery thirty-four, whilst the churchyard gave seventy.

Within doors we find that the number of micro-organisms suspended in the air depends, as we should have expected, upon the number of people present, and the amount of disturbance of the air which is taking place. In illustration of this the following experiments made at one of the Royal Society's conversaziones held at Burlington House last year may be mentioned. At the commencement of the evening, when a number of persons were already present, and the temperature was at 67° Fahr., the two gallons of air examined yielded 326 organisms; later on, as the rooms became densely crowded, as indicated by the temperature rising to 72° Fahr., the number reached 432. The next inorning, on the other hand, when the room was empty, the air yielded only 130, but even this is doubtless in excess of the number which would be present in the room in question under normal conditions, in which, judging from experience, I should expect to find about 40 to 60 in the same volume of air. Again, I found that the air in the large entrance hall of the Natural History Museum in Cromwell Road yielded under ordinary conditions from 50 to 70 organisms in the same volume, but on Whit Monday, when an immense number of visitors were present in the building, I found as many as 280. Again, on a paying day at the South Kensington Museum, I found about 18, but on the Saturday, when no entrance fee is charged, there were as many as 73 organisms present in the same volume.

As an instance of the immense number of microbes which may under given circumstances be found suspended in the atmosphere, the following experiments, showing the number falling on one square foot in one minute, may be mentioned. The first experiment was made in a railway carriage (third class) on a journey from Norwich to London. Soon after leaving Norwich I tested the air; there were at the time four persons in the carriage, one window was closed, the other open, and the experiment was made near the open window. I found that under these conditions 395 organisms were falling on the square foot in one minute. On reaching Cambridge, the carriage was taken possession of by a number of men returning from Newmarket races, and remained quite full (ten persons) to VOL. XXII.-No. 126.



London. About halfway between Cambridge and London I made a second experiment, one window being shut, and the other was only open four inches at the top; the air was tested near the closed window, with the result that no less than 3,120 organisms were found to be falling on the square foot in one minute. On another occasion I made an experiment in a barn in which flail-threshing was going on. The atmosphere was visibly laden with dust, and on testing it I found that upwards of 8,000 organisms were falling on the square foot in one minute. It would probably be difficult to find a place in which the number of suspended microbes was greater than this, the great abundance of bacterial life in the material under treatment, the dryness of the latter, and the violent commotion occasioned by the threshing being all highly conducive to the distribution of an enormous multitude of micro-organisms throughout the air.

The careful study of the various micro-organisms present in air has hitherto received but little attention; it is, however, well known that important functions are performed by them in the laboratory of nature, but only in very few cases has any particular action been identified with a specific micro-organism. Apart from the theoretical interest attaching to the particular work performed by specific microorganisms, there is the question of the influence which is exerted by these micro-organisms on health. Now, although there have been so far practically no organisms discovered in air which are known to be connected with any of the diseases to which man is subject, yet there cannot be a doubt that, in the immediate vicinity of the foci of infection, such harmful organisms are present, and that their distribution and conveyance through the atmosphere must take place in just the same manner as in the case of those micro-organisms which we have been considering. It is, moreover, this familiarity with the circumstances which are favourable or unfavourable to the dissemination of micro-organisms in general which should guide us in avoiding distributive influences coming into play in cases of zymotic disease and in the management of the sick-room generally. Thus it was from considerations of this kind that the principles of antiseptic surgery were laid down by Sir Joseph Lister. The manner in which the presence of micro-organisms in air should be regarded has been recently most concisely described by Professor Burdon Sanderson in the following words:

Considering that we know the living dust of the air does contain organisms which are capable of producing putrefaction and inflammation in wounds-for that is a thing about which we are certain-and that it may contain the distinctive or specific poisons of particular diseases; therefore, just as when rabies is prevalent amongst dogs all dogs should be taken care of, or as in countries where there are poisonous snakes care is taken to keep all snakes out of houses, so it behoves every one to be as careful as possible to maintain the air as free as possible from these

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