APPENDIX E. cxlvii 



of living units, whilst those of the next great class are not \ 

 The tendency in the former is towards death ; the tendency 

 in the latter towards recovery. The non-parasitic infective 

 or specific diseases are also partly local and partly general 

 affections. The local affections are closely allied to other 

 morbid states, such as cancer and tubercle, with which they 

 are not usually classed. Many of these local diseases tend 

 to become general diseases. Similar morbid growths spring 

 up in various parts of the body, and the blood itself becomes 

 affected. They are also more or less apt to spread from 

 individual to individual. All are capable of being generated 

 de novo. Such local affections are united by the closest 

 bonds of similarity to the more general zymotic diseases, 

 amongst which all degrees of contagiousness are manifested. 

 The members of the whole series, however, are intimately 

 related to one another; and their mode of propagation is 

 essentially similar, even though the readiness with which 

 contagion occurs is variable. Very many of them are un- 

 doubtedly generable de novo; and the others are probably 

 also capable of arising ' spontaneously,' though the proof of 

 this, on account of their highly contagious nature, is difficult 

 to establish. 



All these latter diseases, therefore, are dependent upon 

 local perverted modes of growth, or upon chemical changes 

 of a definite, though unknown, character taking place in the 

 blood — partly under the influence of general causes, and 

 partly owing to the initiation of chemical changes induced 

 by contact-action of contagious particles or fluids. As with 

 diseases in general, so with these, two sets of factors are 



^ A more complete investigation (since the delivery of this lecture) 

 of the facts known concerning parasitic diseases has led me to make 

 certain important modifications in the view above expressed as to the 

 role of the parasites in these aftections, as may be seen by reference to 

 Chap. xix. 



k 2 



