16 INFLAMMATION. 



pally which are exposed to external influences, while those of 

 the other class occur by preference in parts and organs to which 

 there is no access excepting through the circulation. These 

 distinctions, however, are not constant, for there are many in- 

 stances in which secondary inflammations affect external parts, 

 and many others in which internal organs are the seat of 

 primary inflammations, as, for example, when nepliritis arises 

 from exposure to cold. Much more important distinctions, 

 however, may be based on a comparison of the structural 

 changes which the two processes determine in the tissues 

 affected ; or, in other words, on their pathological anatomy. In 

 making this comparison, there is one important principle to be 

 borne in mind : In all injlammations, the form of the lesion is 

 dependent on that of the area of influence of the injury. Thus, 

 in those cases of primary inflammation in which it may be 

 supposed that an impression received by afferent nerves distri- 

 buted to mucous or cutaneous surfaces, is reflected to internal 

 organs (as in the case of nephritis from cold, already referred to), 

 the area of influence of the injury is wide enough to comprise 

 whole organs, and the resulting lesions are of corresponding 

 extent. In the strictly local inflammations, the correspondence 

 in form between cause and effect is, of course, closer and more 

 obvious, the area of. a traumatic inflammation being larger than 

 that of the injury which produces it, but of exactly similar form. 

 As regards infective inflammations, the correspondence is not so 

 plain, but the consideration of their pathological anatomy is 

 sufficient to satisfy us that it is equally complete. It is the 

 anatomical character of all infective inflammations that the 

 lesions to which they give rise are disseminated rather than 

 diffused. Particles of matter, of the nature of which we can 

 assert nothing, excepting that they are of extreme minuteness, are 

 conveyed from a primarily inflamed part to other parts previously 

 healthy, and become foci of infective induration or suppuration 

 (miliary tubercles, pysemic abscesses), each of w^hich is the pro- 

 duct — if one may be allowed the expression — of a single seed." 



VAlilETIES OF INFLAMiMATION DUE TO CAUSATION. 



And to quote from the same author on this subject : — 

 " Although if we be careful to distinguish what is essential to 



