34 THE LOCAL LESION 



and the degree of the immunity. For example, in severe and 

 rapidly fatal infections from post-mortem wounds i.e. t where the 

 infection is virulent and the immunity but slight there is very 

 little local reaction and very little glandular enlargement, the 

 process being septicaemic from the first. Where the infective and 

 protective forces are equally matched the local lesions are more 

 developed ; inflammation, and usually suppuration, occur at the 

 site of the wound, and the glands enlarge and may suppurate ; 

 and when the infection is so feeble as to be quite unable to cope 

 with the immunity, the local lesion is the sole result of the infec- 

 tion. Eyre gives a similar example in the results of injecting 

 similar doses of pneumococci into rabbits of different ages. The 

 young animal is most susceptible, and in it death occurs within 

 forty-eight hours from septicaemia, and there is but little local 

 reaction. In half-grown animals the local lesion is more developed, 

 and is gelatinous or fibrinous, containing many leucocytes, and 

 the animal lives several days. In old rabbits quite definite pus is 

 formed, and the animal lives longer, and may recover completely. 

 Hence suppuration may be regarded as a proof that the defensive 

 and infecting forces are fairly balanced, and that either may be 

 victorious in the conflict. 



The other local lesions need not be discussed at length, but the 

 case of tubercle and the allied diseases requires a brief notice. 

 Here the lesion indicates the presence of a very considerable 

 degree of immunity to the toxin, for the structure of a tubercle is 

 exactly similar to that of the cellular reaction to many feebly 

 irritating foreign bodies e.g. t unabsorbable ligatures, substances 

 from which it is clear no potent toxin can be given off; but it 

 also indicates that there is a defect in the mechanism by which 

 the bacilli should be removed, since the process is (for a time at 

 least) a progressive one. Here the walling-in of the infected area 

 which occurs as the result of the reaction of the tissues may be 

 taken to be a defensive process, but, as we shall have occasion to 

 see, it is one of doubtful utility. 



EARLY THEORIES OF IMMUNITY. Before turning to the dis- 

 cussion of the nature of immunity in the light of our present 

 knowledge, it will be convenient to insert a short account of some 

 of the early theories of the subject, which are in the main of 

 historic interest only. They have served their purpose as a point 

 of departure for subsequent research. 



Of such nature was Pasteur's theory of exhaustion, the earliest 



