RESPIRATION 327 



to the engine fires burning badly. The passengers could partly 

 protect themselves by closing the windows ; but the engine drivers 

 were liable to become unconscious, and at least one very serious 

 accident occurred, owing to a train running on with the men on the 

 engine unconscious. 



In the London Underground Railway there was also much 

 trouble, owing to the great traffic, although there were numerous 

 openings to the street along all parts of the system, and a colliery 

 fan had also been installed at one point. The difficulties were 

 referred to a Board of Trade Committee of which I was a member, 

 , and I made numerous analyses of the air.^^ It was never so bad 

 as appeared to have been sometimes the case in the Apennine tun- 

 nels, and the trouble from sulphuric acid and smoke was largely 

 mitigated by the use of Welsh steam coal containing very little sul- 

 phur. The air was often, however, very unpleasant, and many 

 persons were unable to use the railway. At busy times the per- 

 centage of CO2 might rise as high as 0.8, and of CO to .06 ; but of 

 course passengers and railwaymen were not long enough exposed 

 to this air to suffer from the effects of CO, and repairing work on 

 the line was not carried out except at night. At the end of the 

 inquiry it was agreed to introduce electric traction, and since this 

 was done there has been no further difficulty. The tunnels are close 

 to the surface, and the trains push abundance of air out and in 



(through openings to the outside air. 

 In the (London) tubes, which lie much deeper, the ventilating 

 action of the trains proved insufficient by itself to prevent the air 

 from becoming rather unpleasant; and systematic ventilation by 

 fans was therefore adopted. In various other railway tunnels 

 simple shafts are provided; and in the Severn Tunnel there is a 

 nearly central shaft provided with a powerful fan. By these 

 means the air is kept fairly pure. 



Air of Sewers. The air of sewers is perhaps mainly of interest 

 in connection with the time-honored belief that "sewer gas" 

 spreads infection. Some of my earliest scientific work was con- 

 cerned with the air commonly present in sewers, and was started 

 by the late Professor Carnelley and myself^^ at the request of a 

 House of Commons' Committee appointed in consequence of alarm 

 as to the sewers of the House of Commons. 



The air of a sewer has, of course, an unpleasant smell, which, 

 however, is hardly noticed except at the manhole by which access 



^Report of the Committee on Tunnel Ventilation, Pari. Paper, 1897, Appendix i. 

 " Carnelley and Haldane, Proc. Roy. Soc, 42, p. 501, 1887. 



