396 SCIENCE PROGRESS 



manufacturing work. No one doubts that the health, efficiency^ 

 and comfort of our working population are matters of the utmost 

 importance. But the desirability of properly investigating the 

 hygienic conditions of various industries is scarcely yet recog- 

 nised as it ought to be. There is plenty of talk and a large 

 number of regulations ; but real knowledge — the indispensable 

 basis of effective action— is too often lacking, and can be gained 

 in no other way than by careful and detailed observation and 

 experiment. This can be illustrated from all branches of 

 hygiene — for instance, by the immensely important knowledge 

 patiently gained during the last few years as to the nature and 

 means of spread of various infective diseases. 



I wish, however, to emphasise the same fact in connection 

 with industrial hygiene ; and perhaps the specific problems 

 just discussed may enable me to do so. They concern the 

 physical and chemical characters of the air in its relation to 

 certain industrial employments. Insufficient study has, in 

 spite of the best intentions, led to many mistakes in connection 

 with these employments. First, as regards work in compressed 

 air, we find on the one hand that divers have been more or 

 less hampered or endangered by that somewhat rare condition, 

 poisoning by carbon dioxide. But if we turn to men employed 

 in compressed air in tunnels, etc., we also find the conditions — 

 in England at least — reversed in a curious way. It has become 

 a common popular belief that, provided the carbon dioxide 

 percentage is low enough, all must be well with any kind 

 of air. For instance, in the case of the large tunnel at present 

 being constructed in compressed air under the Thames at 

 Rotherhithe, London, the County Council, regardless of the 

 enormous expense, has prescribed that, in view of the danger 

 of caisson disease, the proportion of CO2 shall not exceed that 

 in the average air outside by more than 4 volumes per 10,000. 

 It is, of course, not conceivable that by increasing the air 

 supply to such an extent caisson disease can be prevented. 

 The chief effect of the large air supply seems to be that the 

 tunnel is very warm, as in consequence of the large quantity 

 of air it is not effectively cooled between the compressors and 

 the tunnel. The large air supply is thus probably doing more 

 harm than good; and the absence of effective regulations for 

 preventing caisson disease lays the Count}' Council open to 

 criticism in view of the long-existing knowledge of the subject. 



