10 COLD, WET, AND FATIGUE 



the more subtle functions of the leucocytes may be similarly 

 depressed by a low temperature. The exposure of the skin to 

 cold, especially if the animal heat be abstracted more quickly 

 by evaporation of moisture on the surface, will lead to a cooling 

 of the blood which circulates through it, and hence to a slight, 

 though appreciable, cooling of the whole blood. This, it is true, 

 is soon compensated for, and no great amount of cooling of the 

 whole body occurs; but even so, it is quite possible that the 

 periodical chilling of the leucocytes during their repeated passages 

 through the cold skin may be sufficient to diminish greatly their 

 functional activity, and to lower the resistance to a point at which 

 infection can occur, and when once pathogenic bacteria have 

 gained a foothold, the resistance will for a time tend to decrease. 

 There is also some evidence going to show that exposure to cold 

 may lessen the production of the defensive substances which occur 

 in the blood (alexin, antibodies, etc.), though this is not fully 

 proved. It is worthy of note that the loss of immunity due to the 

 action of cold and wet on one part of the body (such as the feet) 

 is a general one, and may result in a nasal catarrh, an attack of 

 pneumonia, acute rheumatism, etc., according to the nature of the 

 infection at hand. It is not necessarily a local infection of the 

 chilled region. This is very well shown experimentally. Fowls 

 are immune to anthrax, but are rendered susceptible if they are 

 kept for some time standing in cold water ; and this acquired 

 susceptibility is then a general one, and not merely of the feet. 



Cold and wet, as is well known, have less action when accom- 

 panied by energetic muscular exercise, so long as this does not 

 reach the extent of undue fatigue. This is not because less heat 

 is lost during exercise. The reverse is the case. The suggested 

 explanation is that the muscular metabolism leads to an increased 

 production of heat, and at the same time the cutaneous capillaries 

 are dilated and the heart accelerated, or that the circulation of 

 blood through the skin occurs quickly ; further, the internal 

 temperature of the body may actually be raised several degrees. 

 The result is that the temperature of any given leucocyte never 

 falls much below normal, if at all, since it comes from the internal 

 regions where the temperature is raised, passes rapidly through 

 the skin, and returns again to the interior of the body. 



The effect of fatigue, either alone or in conjunction with cold and 

 wet, is also well known, and is one reason for the excessive mor- 

 tality from disease of armies in the field. It is less explicable, 



