3B6 



NATURE 



[March r, 1877 



I found that suspended particles of sal ammoniac subsided in an 

 atmosphere of hydrogen scarcely twice as fast as in atmospheric 

 air. 



Thus an atmosphere fourteen times as rare as that of London 

 (and, as Pro*". Stokes remarked, possessing only half the viscosity 

 of air), still offers sufficient resistance to the subsidence of minute 

 suspended particles to prevent them from falling more rapidly 

 than one inch per minute. Such particles could not therefore be 

 left behind by an ascending current of the slightly rarefied but 

 more viscous air produced by an increase of temperature to 

 100° C. 



In addition to these aqueous and other volatile particles which 

 disappear by a gentle heat, there are also others which consist 

 partly of organic and partly of mineral matters. But the 

 organic seem greatly to preponderate in the air of towns, because 

 such air becomes apparently perfectly clear after it has been 

 ignited. 



The processes of fermentation, putrefaction, and decay afford 

 abundant evidence that zymotic and other living germs are pre- 

 sent amon-jst the organic portion of the suspended matters, whilst 

 many analyses of rain-water, made by myself and others, show 

 that the salts of sea-water are amongst the mineral constituents 

 floating in the atmosphere. 



Of the zymotic matters, those which produce disease in man 

 are obviously of the greatest importance. The outbreak of 

 Asiatic cholera in Southampton in the year 1866, for instance, 

 was traced by the late Prof. Parkes, F.R. S., to the dispersion 

 of infected sewanje through the air. The sewage became infected 

 by the intesLinal discharges from some cholera patients who 

 landed from the Peninsular and Oriental Company's steamship 

 Poonak. 



In this case the dispersion was produced by the pumping of 

 the infected sewage and its discharge, in a frothy condition, 

 down an open channel eight or nine feet long. The efifluvium 

 disengaged from this seething stream was described as over- 

 powering, and was bitterly complained of by the inhabitants of 

 the adjacent clean and airy houses, amongst whom a virulent 

 epidemic of Asiatic cholera broke out a few days after the 

 se«rage received the infected dejections. Nevertheless the dis- 

 charge of the frothy liquid was kept up day and night for about 

 a fortnight, and 107 persons perished. At length a closed iron 

 pipe was substituted for the open conduit ; from that day the 

 number of cholera cases diminished, and within a week of the 

 protection of the conduit the epidemic was virtually over. 



In this example a potent cause of the suspension of the zymotic 

 poison in the air was obvious, but in the many alleged instances 

 of the propagation of typhoid fever by sewer gases, the condition 

 of dispersion is not so evident. Does the flow of sewage in a 

 properly constructed sewer produce sufficient agitation to dis- 

 perse liquid particles through the air-space of the sewer? I 

 endeavoured to answer this question by violently agitating a 

 soluti jn of lithic chloride in a glass cylinder three inches in 

 diameter and thirty inches high, with a wooden rod, and ascer- 

 taining whether the atmosphere at the mouth of the cylinder 

 became impregnated with the liquid, by testing it with the flame 

 of a Bunsen burner ; but no trace of lithium could be detected at 

 the mouth of the jar, even after an agitation much in excess of 

 what would ordinarily occur in a sewer. 



There is, however, another kind of agitation to which sewage 

 is subject that may produce a very different result — I allude to 

 the development of gases during the processes of fermentation 

 and putrefaction. It is well known that the bursting of minute 

 bubbles of gas at the surface of an effervescing liquid causes the 

 projection of visible liquid particles into the air to the height of 

 several inches. Such visible particles are seen to fall back again 

 immediately into the liquid ; but it appeared to me not unlikely 

 that other particles, too minute to be seen, might be simul- 

 taneously projected, and by reason of the smallness of their 

 masses in relation to their sectional areas, might continue sus- 

 pended in the air for a long time. To ascertain the fallacy or 

 truth of this notion I made the following experiment : — 



A quantity of a strong solution of lithic chloride was placed in 

 a shallow basin and acidulated with hydrochloric acid ; fragments 

 of white marble were then added, and a paper tube five inches 

 in diameter and five feet high was placed vertically above the 

 basin. So long as the effervescence continued, abundance of 

 particles of lithium were visible in a Bunsen flame held at the 

 upper end of the tube. A tinplate tube three inches in diameter 

 and twelve feet long was now placed in such a position as to 

 bring one of its open ends over the top of the paper tube. The 

 tin tube was nearly horizontal but slightly inclined upwards from 



the paper tube, so as to cause a gentle draught of air to pass 

 through it, when it was slightly heated externally near its lower 

 extremity. A Bunsen flame placed at the end of this tube 

 furthest away from the effervescing liquid, showed that the sus- 

 pended particles of solution of lithic chloride were not perceptibly 

 less numerous than at the mouth of the paper tube ; neither 

 were they much diminishei at the further end of the tin tube 

 when the height of the paper tube was increased to nine and a half 

 feet. There can, I think, be little doubt that these particles, 

 v/hich had thus been carried along by a gentle current of air for 

 a distance of twenty-one feet, would be similarly conveyed to 

 very much greater distances. 



The following conclusions as to the behaviour of flowing sewage 

 may be drawn from these experiments : — 



1. The moderate agitation of a liquid does not cause the sus- 

 pension of liquid particles capable of transport by the circum- 

 ambient air, and therefore the flow of fresh sewage through a 

 properly constructed sewer is not likely to be attended by the 

 suspension of zymotic matters in the air of the sewer. 



2. rhe breaking of minute gas-bubbles on the surface of a 

 liquid consequent upon the generation of gas within the body of 

 the liquid is a potent cause of the suspension of transportable 

 liquid particles in the surrounding air, and therefore when, 

 through the stagnation of sewage or constructive defects which 

 allow of the retention of excrementitious matters for several days 

 in the sewer, putrefaction sets in and causes the generation of 

 gases, the suspension of zymotic matters in the air of the sewer 

 is extremely likely to occur. 



3. It is therefore of the greatest importance to the health of 

 towns, villages, and even isolated houses, that foul liquids should 

 pass freely and quickly through sewers and drain-pipes, so as to 

 secure their discharge from the sewerage system before putrefac- 

 tion sets in. 



Linnean Society, February i. — Mr. G. Bentham, F.R.S., 

 vice-president, in the chair. — Messrs. G. Boulgej, Alfred S. 

 Heath, and William Meiler, were elected Fellows of the Society. 

 — Mr. A. W. Bennett exhibited, and made remarks on, certain 

 specimens of insects illustrating mimicry ; these had been cap- 

 tured in Syria by Mr. N. Godman. — An unusual form of double 

 anemone, and some excessively large oak-leaves gathered near 

 Croydon, were shown by Mr. S. Stevens, and they evoked dis- 

 cussion from the Chairman and other Fellows present. — Sir John 

 Lubbock then proceeded with Part 4 of his contributions on the 

 habits of ants, bee?, and wasps. In this communication he 

 illustrated by ingenious experiments his modus operandi of test- 

 ing their faculties, dispositions, habits, &c. , by something of a 

 doublf: F apparatus ( R), whereby an interval of three-tenths 

 of an inch, either by a drop from above or reaching upwards the 

 distance from below, alone prevented ants from gaining access to 

 a covered glass cell filled with larvse. They evidently had not 

 the acumen to surmount the three-tenths of open space, although 

 they had lor hours before been traversing the route and carrying 

 off larv32 previous to the small gap being made. Industry was 

 conspicuously shown by one specimen, which Sir John used to 

 place in solitary confinement in a bottle for hours, and once for 

 days, but the moment released it commenced its labjriouslarvse- 

 gathering propensities. It seems, fro.ia other experiments, that 

 ants in difficulties within sight of their companions are by no means 

 always assisted or relieved, other attractions, food and such like, 

 possessing greater interest for them. On putting some specimens 

 under the influence of chloroform, little or no notice was taken of 

 those insensible by their companions, the tendency apparently being 

 to let friends lie and throw over the edge of the board strangers 

 thus chloroformed. It seems that to get ants properly intoxi- 

 cated with spirit for experimental purposes is no easy matter, 

 some recovering too quickly, and others remaining so thoroughly 

 dead drunk as to come under the rank of impracticables ; while 

 between reeling friends and strangers the experimenter finds 

 himself baffl:d. The sober ants are exceedingly puzzled at 

 finding their friends in such a condition. As a general rule they 

 picked up drunken friends and carried them to the nest, whilst 

 they threw into the water and drowned strangers. In some in- 

 stances confusion arose, for a few of the strangers were carried 

 to the nest and friends tumbled into the water, but they did not 

 return to the rescue of the friends, though strangers were after- 

 wards expelled from the nest. Sir John expresses surprise that 

 ants of one nest perfectly well know each other. Even after a 

 year's separation old companions are recognised and amicably 

 received, whereas strangers, particularly among the Lasius Jlavus, 

 are almost invariably attacked and msdtreated, even when intro- 



