Seasonal Bacteria in Air of Dwellings 53 



that found in the open air. The same increase from win- 

 ter to summer, and decrease from summer to autumn 

 are present, — an evidence that the relative influence of 

 heat, moisture and sunshine is the same in the city as 

 it is in the country. 



In human dwelUngs, also, the bacteria in the air are 

 readily affected by seasonal changes. In this instance, 

 however, the differences do not run parallel to those 

 obtained in relation to the open air. Examinations of 

 the air in Paris hospitals demonstrated that there was 

 a steady decrease in the number of bacteria from March 

 to August, and a steady increase from August to Novem- 

 ber. These apparent discrepancies find a ready ex- 

 planation in the fact that the open windows during the 

 warm months allowed a more thorough ventilation of 

 the hospital rooms, and, therefore, a more rapid removal 

 of the organisms suspended in the air. An important 

 point in this connection is the large n.umber of bacteria 

 found in the air of hospitals. It is safe to assume that 

 a considerable portion of the organisms suspended there 

 were pathogenic, and that they were a source of infection 

 to the patients and attendants. 



The influence of climate. — It is a self-evident truth 

 that the number of bacteria in the atmosphere of any 

 region bears a direct relation to the climate of that region. 

 In warm tropical countries with an abundance of rain- 

 fall, the multiplication of bacteria in the soil, water, 

 and all vegetable and animal matter proceeds with great 

 rapidity. Under such conditions, the particles of dust 

 raised from the earth's surface carry an abundant num- 

 ber of bacteria and enrich the atmosphere to a very 



