394 THE POPULAR SCIENCE MONTHLY 



is accelerated, the blood is sent in increased volume to the skin, and 

 circulates there in far greater volume, while less goes through the 

 viscera and brain. As the surface temperature rises, the cutaneous 

 vessels dilate, the veins become filled, the arteries may become small in 

 volume, and the blood-pressure low, the heart is fatigued by the extra 

 work thrown upon it. The influence of the heat stagnation is shown 

 by the great acceleration of the pulse when work is done and the 

 slower rate at which the pulse returns to its former rate on resting. 



The increased percentage of carbonic acid and diminution of 

 oxygen which has been found to exist in badly ventilated churches, 

 schools, theaters, barracks, is such that it can have no effect upon the 

 incidence of respiratory disease and higher death-rate, which statistical 

 evidence has shown to exist among persons living in crowded and 

 unventilated rooms. The conditions of temperature, moisture and 

 windless atmosphere in such places primarily diminishes the heat loss, 

 and secondarily the heat production, i. e., the activity of the occupants, 

 together with total volume of air breathed, oxygen taken in and food 

 eaten. The whole metabolism of the body is thus run at a lower plane, 

 and the nervous system and tone of the body is unstimulated by the 

 monotonous, warm and motionless air. If hard work has to be done 

 it is done under conditions of strain. The number of pathogenic 

 organisms is increased in such places, and these two conditions run 

 together — diminished immunity and increased mass influence of in- 

 fecting bacteria. 



The volume of blood passing through, and of water vapor evapo- 

 rated from, the respiratory mucous membrane must have a great 

 influence on the mechanisms which protect this tract from bacterial 

 infection. While too wet an atmosphere lessens evaporation, a hot 

 dry atmosphere dries up the mucous membrane. As the immunizing 

 powers depend on the passage of blood plasma into the tissue spaces, 

 it is clear that a proper degree of moisture is important. The tem- 

 perature, too, must have a great influence on the scavenger activity of 

 the ciliated epithelium and leucocytes in the mucous membrane of the 

 nose. 



In the warm moist atmosphere of a crowded place the infection 

 from spray, sneezed, coughed, or spoken out, is enormous. On passing 

 out from such an atmosphere into cold moist air the respiratory 

 mucous membrane of the nose is suddenly chilled, the blood-vessels con- 

 stricted and the defensive mechanism of cilia and leucocyte checked. 

 Hence the prevalence of colds in the winter. In the summer the 

 infection is far less. We are far more exposed to moving air, and the 

 sudden transition from a warm to a cold atmosphere does not occur. 

 We believe that infection is largely determined by (1) the mass influ- 

 ence of the infecting agent; (2) the shallow breathing and diminished 



