314 The Water Supply of London, [July 5 



which further inquiry would probably lead to discovery. In the 

 first place we find cholera making its appearance in various localities, 

 healthy or otherwise, and frequently without any apparent cause. 

 Such sporadic attacks occur equally in large towns and in_ isolated 

 hamlets : as a rule, they carry off the first victim and one or two of 

 his friends or neighbours, whose contact, either direct or indirect, with 

 his dejections can frequently be traced. The disease, however, does 

 not spread farther, but soon becomes extinct, to break out again 

 perhaps in a similar manner after the lapse of weeks or months. In 

 this way, isolated attacks were continually occurring during the 

 summer and autumn of 1866 in Manchester and Birmingham, as 

 well as in scores of small villages and isolated hamlets scattered 

 throughout the whole United Kingdom. Such irregular and 

 sporadic assaults powerfully suggest the presence of a specific 

 poison in the atmosphere suspended as impalpable spores or germs, 

 not therefore obeying the law of the diffusion of gases, but de- 

 pending upon currents of air for then transport from place to place ; 

 in fact, behaving exactly like the spores of green moiild or those of 

 the fungus known to gardeners as damp, both of which have so 

 completely taken possession of our atmosphere, that there is pro- 

 bably not a cubic foot of air near the earth's surface which does not 

 contain numbers of them. But these germs, though present every- 

 where, cannot grow and reproduce themselves except under certain 

 favourable conditions. Place a piece of ealf's-foot jelly in a dry 

 atmosphere and it will not become mouldy, but a few hours' sojourn 

 in a damp closet will inlalhbly cover it with a perfect forest of vege- 

 tation. Again, let a geranium be placed in the open air or in a 

 well- ventilated and well-lighted conservatory, and its leaves and 

 stems will continue green and healthy, but let either the light or 

 ventilation be bad, and the plant " damps,'' that is, it becomes covered 

 with a fungus which rapidly destroys its vitality. Thus both kinds 

 of vegetable spores are incapable of verification without certain 

 favourable conditions, which are moreover peculiar for each descrip- 

 tion of organism. 



The cholera poison, if present in the atmosphere, doubtless also 

 requires a favourable conjunction of conditions to render its develop- 

 ment possible. If one of these conditions be absent, the concurrence 

 of all the others is insufficient to produce the effect. Thus, it is 

 highly probable that in the case of cholera, as in that of other 

 epidemic diseases, there are many individuals who, during the time 

 of the epidemic at least, are in such a condition of body as to be 

 absolutely incapable of taking the disease, even if every other 

 favourable circumstance be present. But besides the bodily capacity 

 for the effective reception of the cholera germ, there appears to be 

 in most, probably in all, cases, one other condition at least neces- 

 sary. This condition may be supplied in food and drink. A young 



