258 MR JOHN A1TKEN ON THE 



most important effect on the condition of our lungs, and one towards which I 

 wish to direct the attention of those who make this organ a special study. 

 There seems to be but little doubt that we have here an explanation of some of 

 the effects of different climates. For instance, what a difference there must be 

 in the amount of dust deposited on the lungs from air breathed at, say, St 

 Moritz or Davos Platz, and at such places as Madeira or other similar health 

 resorts ! These remarks are altogether apart from the question of the amount 

 of dust in the air at the different places, and refer only to the action of the 

 lungs on the dust which maybe present.* In the Alpine resorts the air is cold 

 and dry, and the tidal air, which flows backwards and forwards through the 

 bronchial tubes, is in the very best condition for preventing the dust coming into 

 contact with their surfaces, as the difference in temperature between the air 

 and the body is great, and the air is also capable of causing a rapid evaporation. 

 Whereas, at such places as Madeira, where the air is hot and moist, the repelling 

 forces are both at a minimum. The effects of these different conditions on the 

 lungs seems well worth study. 



In illustration of the protective influence of heat and moisture many experi- 

 ments may be made, but the following is perhaps the easiest. Take an ordinary 

 paraffin lamp, raise the flame till a very dense cloud of smoke rises from it. 

 Over the lamp place a very tall metal chimney, to produce a quick current 

 of air and also to cool it. Have ready two porous cylindrical jars (porous 

 jars are used because they keep up a supply of water for evaporation), one 

 jar filled with water slightly heated, and the other with cold water. Cover 

 both jars with wet white paper. Now introduce the hot one into the top of the 

 chimney, and leave the black wreaths of smoke to stream over it for say half a 

 minute, then take it out and put in its place the cold one, and leave it for the 

 same length of time. The result will be, the hot one will be quite clean, not a 

 speck of soot on it, while the cold one is covered with soot. It is not, however, 

 so black as a cold dry surface would be, as the slight evaporation from its 

 surface tends to protect it. 



We must not, however, suppose that the lung surfaces are so well protected 

 as the paper in this experiment. In the lungs the currents are quicker, 

 they do not flow over such uniform surfaces, and further, they pass round 

 curves, so that in the lungs dust tends to deposit where the currents flow 

 quickly where they strike on the concave side of curved passages and on pro- 

 jecting edges. Further, all dust which penetrates beyond the tidal air and gets 

 into the residual air will ultimately fall on the surfaces of the tubes and air- 



■ The amount of dust breathed by invalids at the two places will not be greatly different, Bfl 

 most of their time is spent in the house, and the air in the rooms at the two places will be nearly 

 equally dusty. The higher temperature inside will slightly reduce the thermal effect, but will not 

 diminish the rate of evaporation. 



