270 BIOLOGICAL PROBLEMS 



1. There is evidence that it lowers resistance to 

 acute disease (especially catarrhs, bronchitis, pneu- 

 monia, and phthisis) and that it favours chronic 

 wasting diseases. 



2. Dr. Ogles's researches demonstrated that of all 

 the male industrial classes those with the lowest death- 

 rates are the classes whose occupations are carried on 

 in the open air. The death-rate from phthisis and 

 diseases of the respiratory organs is greatly less 

 among them than the rest of the male community; 

 indeed, agricultural labourers furnish but half of the 

 average adult male mortality from consumption ! The 

 differences in food and housing cannot possibly 

 account for this much greater freedom from pulmonary 

 disease. 



3. The excessive incidence of pulmonary disease 

 (exceeding 50 per cent) on the inmates of back-to- 

 6ack houses, in which there can be no through-venti- 

 lation and useful circulation of air, has been well 

 established by Tatham and others. Dr. Tatham's 

 investigations at Salford were very thorough and 

 exact. He found that in districts where all the houses 

 were built on the vicious system known as " back- to- 

 back", the phthisis death-rate was 5.2 per iboo living; 

 where 56 per cent of the houses were so built, the rate 

 was 3.6; where 23 per cent only were so constructed, 

 it was further reduced to 3.3; and, lastly, where there 

 were no " back-to-back" houses that is to say, where 

 all the houses were provided with some means of light 

 and air both in front and to the rear the rate was 

 only 2.8 per 1000. These results are all the more 

 remarkable because, with the exception of the absence 

 of means for through-ventilation, the back-to-back 

 houses on the whole were, in Dr. Tatham's opinion, 

 in better sanitary condition than the other houses. 



4. During the past half-century there has been a 



