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attenuating agent, or, in other words, as an agent for re- 

 ducing the parasitic virulence of germs. For it may be 

 suggested that the ability or habit of a ferment to tear highly 

 complex organic compounds to pieces, so to speak, in order 

 to procure the oxygen which, under other circumstances, it 

 would obtain in tlie free state, is a kind of parasitic quality. 

 Philosophically the anaerobic which feeds upon dead organic 

 matter may be considered as an intermediate between the in- 

 nocent aerobic saprophyte and the deadly anaerobic parasite 

 which feeds upon the living tissues or fluids. Therefore the 

 question presents itself whether the presence of free oxygen 

 and the proportion in which it is present with other gases, 

 may be regarded as having really an educational influence 

 upon the innocent saprophyte. In an early report on 

 graveyards Mr. David Chadwick mentions a case of a man 

 having been struck dead by a single puff of air from a 

 long-closed vault in which the dead had been interred, 

 whereas no such accidents happen in country churchyards. 

 Again, Dr. Angus Smith has called our attention to the fact 

 that the emanations from moving waters like the Clyde, 

 open to the free air, though they may cause sickness, do not 

 cause fevers ; whereas the emanations from covered sewers, 

 where the atmosphere will have a very different character 

 to that over the Clyde, and from closed tombs and vaults, 

 do cause fevers, and, as in the case mentioned above, even 

 sudden death. But surely we cannot assume that the spe- 

 cific germs of typhoid, say, deliberately remain in the sewer 

 and shun the river; or that specific agents of decay enter 

 the vault beneath the city church and shun the country 

 churchyard. We can scarcely draw a line beyond which no 

 disease germ will venture to go. After all, therefore, the 

 difference between the typhoid germ in the sewer and the 

 germs in the river, the ferments in the country churchyard 

 and those in the unventilated vault, is one of virulence ; in 

 other words, the river germ is an attenuated germ, and the 



