762 METABOLISM 



the floor level; open fires, properly flued modern gas fires, and electric 

 heaters at floor level are the best methods to attain this. 



Suppose the person subjected to conditions which cause the mucous 

 membrane to become swollen and congested should go outside, then the 

 membrane at once becomes pale because the blood vessels constrict, but 

 for some time it remains swollen and boggy and continues to show pitting 

 with a probe. It is while in this state that it offers favorable conditions 

 for the growth of bacteria. The membrane is swollen and covered with 

 secretion, and the blood flow is cut down. The natural defensive agen- 

 cies that are normally carried by the blood do not succeed in combating 

 the multiplication of the bacteria in the swollen membrane. After some 

 time out of doors the blood supply returns because it is required to warm 

 up the cool air, but this reaction does not occur before the mucosa has 

 regained its normal condition.* 



The protective influence of a rapid blood flow through the nasal mem- 

 brane is possibly the explanation of the relative immunity from infec- 

 tious colds of those who work in air containing irritating gases, such as 

 workers in various kinds of chemical factories. Even the irritation set up 

 by coal dust may, by similar methods, afford some protection against in- 

 fection by the tubercle bacillus for phthisis is relatively infrequent 

 among coal miners. The supposedly antiseptic action of ozone is prob- 

 ably due to a similar irritating effect. Any benefit that may be derived 

 from its presence in the atmosphere can not otherwise be explained. It 

 is possible that a useful prophylactic practice to avoid infection, such as 

 that of influenza, would be to stimulate the nasal mucosa at intervals by 

 snuff, but this may be an unwise suggestion. 



After becoming acclimatized to outdoor conditions, the nasal mucous 

 membrane is in a much more favorable condition to withstand infection 

 than indoors because of the very rapid blood flow that is necessary in or- 

 der to supply heat with which to warm up the inspired air. This more 

 rapid blood flow, and the freer flow of lymph which accompanies it, is 

 reinforced by increased secretion, which assists to wash away invading 

 bacteria. Mass infection being equal inside and outside, the animal body 

 can withstand it much less satisfactorily in the former case. 



Many other observations bearing on the relationship between chilling 

 and immunity to infection have been recorded, but it would take us be- 

 yond our subject to discuss them here. Because of their accuracy and the 

 excellent control of possible fallacies, it is important, however, to say 

 something about the recent investigations of Mudd and Grant. 73 These 

 observers measured the temperature of the mucous membranes of the 

 palate, tonsils and pharynx by means of thermo-couples before and dur- 



*The congestion of the mucous membrane brought about by warm moist air does not probably 

 depend on dilatation of the small arteries entailing- increased flow of blood, but rather on dila- 

 tation of the capillaries and therefore a stagnation of blood. 



