180 president's address — SECTION 1. 



4. The control of streets, including tramways, lighting, &c. 



5. The provision of public parks and recreation gi-ounds and 

 other such like measures. 



The time at our disposal forbids much illustration of the work 

 thus summarised, but I will shortly notice some of the measures 

 taken. 



III. 



MEASURES FOR SECURING THE PURITY OF THE AIR. 



In the lirst place it is necessary that the condition of the air be 

 known. It is liable to pollution both from what may be called 

 natural and artificial causes. Thus the air of a swamp is unwhole- 

 some by reason of excessive humidity, and by the results of 

 vegetable decomposition. If a town be built on the swamp, to 

 these natural causes of impurity are superadded those resulting 

 from human occupation. If the town be built on a dry site, these 

 latter causes may be the only ones to be dealt with. Special 

 meteorological, climatological, and microscopic observations not 

 only furnish information of conditions affecting health, out also, 

 when properly understood, may give direction to the efforts to be 

 made with the object of avoiding or controlling changes of con- 

 dition of the air caused by human occupation. So far microscopic- 

 examination of the air does not seem to have yielded practical 

 information to the health officer except in connection with hospital 

 treatment. In the open air the change of condition caused by 

 human occupation is strikingly shown by comparison of town with, 

 country air. Records are available for a number of years in con- 

 nection with, the urban observatory at the Hotel de Ville of Paris, 

 and the suburban observatory at Montsouris in a park of about 

 350 acres. The mean of the observations for the ten years ending- 

 1890 gives 345 as the number of bacteria in a cubic metre of air 

 at Montsouris, to 4,790 at the Hotel de Yille. I have called this 

 "a change of condition" rather than pollution in a morbific sense, 

 as, though it is difficult to suppose that a large quantity of vege- 

 table organism can exist in the air without aft'ecting its wliolesome- 

 ness, so far no direct relationship has been observed between the 

 prevalence of disease of any kind and the bacteriological condition 

 of the air. The Paris observations are published for every Avcek 

 with tables of the deaths from zymotic diseases and diseases of the 

 respiratory organs, and no series of coincidences can be remarked. 

 Very often there is a sudden rise or fall in the mean number of 

 bacteria found in one week as compared with the preceding — the- 

 differences being sometimes equal to 500 per cent. — without any 

 corresponding rise or fall in the death rate of either the week itself 

 or of any subsequent one. Furthermore, after making allowance 

 for the existence in the same arrondissement, the XIV., as that in 

 which is the park of Montsouris, of the great hospital of the 



