1903.] on Civilisation and Health Dangers in Food. 249 



about 28 grains, of arsenic per pound. It was natural to expect that 

 such an amount of arsenic in soot would lead to a distinct contamina- 

 tion of the atmosphere of a town such as Manchester, where soot 

 abounds. This, early in 1901, I found to be actually the case in 

 Manchester,for I discovered that dust deposited from the atmosphere in 

 inhabited rooms, in uninhabited lofts, upon the leaves of trees and 

 shrubs, contained very material amounts of arsenic. 



During the month of March 1902 there was a heavy fall of snow 

 in Manchester,this was immediately followed by a heavy fog lasting one 

 day. The snow, which was perfectly white before, was grey after the 

 occurrence of the fog. I collected the superficial snow over a surface 

 measuring exactly one meter square, and, from the quantity found in a 

 sample of the snow water, calculated that during a single day about 

 0*0000132 grammes of arsenic had been deposited on the small patch 

 of snow under investigation. What may be the effect of the continual 

 breathing of air containing frequently a distinct trace of arsenic ? I 

 cannot say, but the fact remains that the existence of large cities is 

 associated with the contamination of the air with many products of 

 which I have indicated only one. To satisfy myself that this infer- 

 ence was correct I collected, under conditions similar to those I had 

 observed inManchester, samples of dust in one of the London suburbs, 

 in the small town of Montreux in Switzerland, and in the open 

 country near Ambleside ; and found that the London suburban dust 

 contained a material amount of arsenic, though less than the dust 

 collected in the centre of Manchester. On the other hand, the dust 

 collected in the Lake district and in Switzerland contained either no 

 arsenic or an inappreciable trace of the poison. 



I do not wish to labour the argument, nor to suggest that the pre- 

 sence of a small amount of arsenic in the air of a town is certainly a 

 source of danger. I wish rather to indicate the insidiousness than 

 the potency of dangers associated with the gradual modification of our 

 surroundings. 



It might appear that air is not a food and should not be introduced 

 into this discourse, but I contend that air and water are as much foods 

 as beef and mutton, for without oxygen and water metabolism is 

 impossible. 



Disposal of Sewage. Pollution of Water and of Shell-Fish. 



!Man in his nomadic state was not troubled with the question of 

 sewage disposal, for then he had a movable home. Now that large 

 populations have become fixed over limited areas, the disposal of 

 sewage has become a problem of such difficulty and magnitude, 

 that it taxes to the utmost the ability of engineers, of municipal 

 authorities, and even of state departments, without speaking of Eoyal 

 Commissions. 



Certain cities are so situated that their sewage has to be thrown into 

 the sea. "Wherever a large number of individuals are congregated, 



s 2 



