CHAP. xvm. VACCINATION A DELUSION. 257 



the blood; and when we consider that breathing is the 

 most vital and most continuous of all organic functions, 

 that we must and do breathe every moment of our lives, 

 that the air we breathe is taken into the lungs, one of 

 the largest, and most delicate organs of the body, and 

 that the air so taken in acts directly upon the blood, and 

 thus affects the whole organism, we see at once how 

 vitally important it is that the air around us should be 

 as free as possible from contamination, either by the 

 breathing of other people, or by injurious gases or par- 

 ticles from decomposing organic matter, or by the germs 

 of disease. Hence it happens that under our present 

 terribly imperfect social arrangements the death-rate 

 (other things being equal) is a function of the popula- 

 tion per square mile, or perhaps more accurately of the 

 proportions of town to rural populations. 



In the light of this consideration let us again com- 

 pare these diagrams of Irish, Scottish, and English 

 death-rates. In Ireland only 11 per cent, of the popula- 

 tion live in the towns of 100,000 inhabitants and up- 

 ward; in Scotland 30 per cent., and in England and 

 Wales 54 per cent.; and we find the mortality from 

 zymotic diseases to be roughly proportional to these 

 figures. We see here unmistakable cause and effect. 

 Impure air, with all else that overcrowding implies, on 

 the one hand; higher death-rate on the other. This ex- 

 plains the constant difference between London and rural 

 mortality, and it also explains what seems to have 

 puzzled the Commissioners more than anything else 

 the intractability of some of the zymotics to ordinary 

 sanitation, as in the case of measles especially, and in a 

 less degree of whooping-cough for in their case the 



