INTRODUCTORY AND GENERAL 13 



power of the body to the common pyogenic bacteria, and that the 

 mere length of an operation should be an indication for the most 

 scrupulous care in antiseptic precautions. It is perhaps con- 

 ceivable that the anaesthetic drug present in the blood may be 

 sufficient to paralyze the leucocytes for a sufficient time to allow 

 bacteria to gain a foothold in the body. 



Certain drugs, of which the most important is alcohol, have an 

 important action in this respect. The liability of alcoholic 

 subjects to pneumonia and some other infective diseases is well 

 known, and in them the prognosis is more than usually unfavour- 

 able. We have but little knowledge of the action of alcohol in 

 this respect. It may be that it acts as a direct inhibitant of the 

 activity of the leucocytes, and it is known to destroy certain 

 delicate defensive substances (alexins and opsonins) which play 

 some part in the defence of the body against microbic invasion, 

 but it is not known whether these effects are actually manifested 

 in the circulating blood. It is also possible that alcohol tends to 

 inhibit the formation of these defensive substances. 



Alcohol tends to lower the temperature of the body by increas- 

 ing the amount of heat lost. It dilates the superficial vessels and 

 accelerates the heart's' action in a way somewhat similar to 

 muscular exercise, but does not, like it, raise the temperature of 

 the interior of the body. Hence the effect of alcohol in conjunc- 

 tion with cold and wet is to increase their ill-effects. More blood 

 is forced through the chilled skin and more heat is lost. The 

 injurious effect of alcohol during exposure to cold is well known. 

 The results, however, are different when alcohol is taken after 

 exposure, and when the sufferer has reached warmth and shelter. 

 There the increased flow in the cutaneous capillaries leads to a 

 warming of the skin and consequent cessation of the chilling of 

 the blood, although the loss of heat may go on. 



Diseases the most important of which are Bright's disease and 

 diabetes lead to a general lowering of the level of immunity, and 

 a consequent predisposition to other diseases. We have no 

 knowledge of the way in which they act. 



There are many causes which act locally, and cause a local 

 lowering of the resistance. Some of these have been hinted at 

 above, but their consideration will be deferred for the present. 



In considering the nature, severity, and prognosis of any disease, 

 two factors have to be recognized : (i) the immunity of the patient, 



