224 DISEASES FROM HARMFUL ORGANISMS 



dust of the air, and so are breathed in more or less con- 

 tinously. The respiratory passages are therefore rarely if 

 ever entirely free from organisms which are capable of 

 causing colds if they get a chance to establish themselves 

 within the body. They are lying in wait, so to speak, so 

 that any relaxation of the resistance of the body enables 

 them to gain a foothold. 



Catching Cold. — It has been long known that a 

 sudden chilling of the body, as from sitting in a draft, is 

 apt to result in a cold. Quite recently, the explanation 

 of this fact has been furnished by the discovery that when 

 the outer surface is chilled rapidly there is caused, by a 

 mechanism which cannot be described here, a partial shut- 

 off of the blood-supply to the mucous membranes of the 

 respiratory passages. This interference with the proper 

 nutrition of the cells reduces their resisting power 

 sufficiently to allow the organisms of colds to establish 

 themselves and to develop. It should be understood that 

 a rapid chilling, rather than simply the fact of being cold, 

 is the condition which is likely to start the infection into 

 activity. However, one should bear in mind that indi- 

 viduals may also be especially susceptible to infection as 

 a result of under-nutrition or of exhaustion, and so may 

 develop colds without there having been any special ex- 

 posure immediately before the attack. Obviously, the 

 best preventive of colds would be to have the respiratory 

 passages free from the organisms which cause them ; since 

 this is not possible in practice, the alternatives are the 

 maintenance of the body in the best possible health and 

 the avoidance of such exposure as is likely to cause rapid 

 chilling of the body surface. The regular taking of cold 

 baths, where good reactions are secured, is an excellent 

 means of keeping high the general resistance against 

 colds. 



Disease due to Higher Fungi is comparatively rare. 

 There is in parts of California what is known as San 

 Joaquin Disease, which resembles tuberculosis of the lungs 



