450 



like manner is unable to effect the necessary change in the 

 pulmonary blood. When mixed with oxygen in the proportion 

 of four to one by measure, it may be much longer respired, 

 but it is with a somnolent and narcotic effect. The various 

 combinations of hydrogen, the common products of animal 

 and vegetable decomposition, are all, indeed, capable of a 

 serious sedative action upon the heart and brain through 

 their influence on the nervous system. In the human excreta 

 and refuse of towns we have a very considerable generation 

 of hydrogen associated with carbon, ammonia, phosphorus, 

 and sulphur, all of which are offensively odorous, and 

 occasionally, when concentrated, fatal in their eftects ; whilst 

 in milder instances they induce nausea, giddiness, and a 

 lethargic depression of the vital powers. Dr. Leeson's late 

 classification of these putrescent vapours is, I think, open 

 to objection, and would convey an erroneous inference as to 

 the true character of these gaseous compounds, inasmuch as 

 he includes carbonic acid and oxide with the remittent and 

 typhoid miasmata under the head of " dangerous, but in- 

 odorous," whilst the combinations of hydrogen are repre- 

 sented merely as offensively " odorous whereas of these 

 relative gases when present in respirable equal quantities, 

 the latter are unquestionably the more pernicious of the two, 

 whether viewed as a chemist or tested in medical practice. 

 It is a doubtful assumption, too, to affirm that typhoid mias- 

 mata are inodorous; for should they, as I think, consist of 

 minute putrid particles held in atmospheric suspension by 

 aqueous vapour, the probability is that they are odorous. 



Carburetted hydrogen, a component of the explosive 

 atmosphere of our collieries, is respirable when mixed with 

 fourteen times its own volume of common air; though colliers 

 as a class, from their mode of labour, bad habits, and foul 

 air, are too often found to be a deformed and short-lived 

 race. All the illuminating gases may in like manner be' 



