Microhic Life in Seirer Air. 207 



have all been destroyed in the process of the putrefactive action 

 which has taken place. This result happens in sewers as well as 

 in dissecting-rooms. 



There are two classes of microbes, which have to do with 

 destructive agencies — the moulds, which belong to the family of 

 fungi, and the true microbe or schizomycites order. If air be 

 sparsely admitted the moulds predominate, and there is a 

 tendency to acid formations, carbonic acid, butyric, nitrous 

 acid, &c. ; but if it is all but excluded, the schizomycites are 

 most numerous, and it is for this reason that ventilation must 

 be good or not at all. We now reach a point of importance in 

 the inquiry. Microbie life is connected with decomposition of 

 organic matter containing nitrogen in its constitution. Decom- 

 position is accelerated or checked by outside circumstances, such 

 as the presence or absence of air ; it is also influenced by tem- 

 perature, by moisture, and the presence or absence of other 

 agencies, as is proved by the action of antiseptics and germicides. 

 We may even advance a step further, and say that without 

 decomposition, there is no development of microbie life ; this is 

 an important factor in the consideration of sewer air. 



Let us now inquire as to the nature of the decomposition 

 whicli promotes the formation of these organisms. As experience 

 is gained we become more and more convinced that there is no 

 known means whereby any such organisms arise without the 

 previous introduction of a parent germ of the same kind ; that 

 the spontaneous origin of such germs is not likely to happen; 

 though no doubt in the case of some kinds of disease germs, 

 such as that of typhus fever, the dormant organism is an ever- 

 present commodity, as much as that which gives rise to the blue 

 mould in cheese. It is also established by experiment that a 

 germ may be made more malignant by cultivation, or by culti- 

 vation may be deprived of its malignancy. It is upon this fact 

 that vaccination is found to be prophylactic against small-pox, 

 and Pasteur is able to prevent the spread of splenic -fever among 

 cattle, and take out the sting of hydrophobia, by giving rise to a 

 disease of a similar but of a milder type, though in the last- 

 mentioned this may be only a choice of two evils. 



Let us now ask whether any microbes are to be found in sewer 

 air ? Secondly, whether they are necessary parts of a sewer 

 system ? Thirdly, whether being there they are benign or malig- 

 nant? And fourthly, whether it is possible for those which are 

 benign to become malignant by cultivation in the sewer or out- 

 side, and vice versa. My attention was first attracted to sewer 

 air in the years 1853, 1854, and 1855. We had a ventilator 

 fixed to the sewer at the Friends' School in 185-i, which was 

 then in Park Lane, Croydon. One of the teachers, who was of 

 an inquisitive turn of mind, got on the roof and smelt at the 



