APPENDIX E. cliii 



changes within the body. As Dr. Carpenter pointed out, 

 nearly twenty years ago, in a very able article on the ' Pre- 

 disposing Causes of Epidemics \' these causes are reducible 

 to one or other of three categories : — ' (i) those which tend 

 to introduce into the system decomposing matter that has 

 been generated in some external source ; (2) those which 

 occasion an increased production of decomposing matter in 

 the system itself; and (3) those which obstruct the elimination 

 of the decomposing matter, normally or excessively generated 

 within the system, or abnormally introduced into it from 

 without.' Now the common characteristic here is that ' any 

 one of these causes will tend to produce an accwnulation of 

 disintegrating azotised compounds, in a state of change, in the 

 circulating current' ; and observation seems to tell us that 

 either of the causes leading to such a result may, when 

 potent, suffice to assist the spread of epidemic diseases, 

 though two or more in combination lead to much more cer- 

 tain results. Much has been done to diminish the prevalence 

 of these conditions — which act only too surely upon the 

 individual in giving rise to 'predisposing' causes of disease — 

 though far more still remains to be done. Happily, however, 

 public attention is now becoming (though slowly) aroused to 

 the importance of pure air, pure water, efficient drainage, and 

 wholesome food, as instruments for maintaining the health of 

 the community. 



But let us not be blinded by any narrow or exclusive 

 theories which would teach us that epidemic and infective 

 diseases cannot arise de novo. Let us, instructed by a broader 

 survey of the facts, assign no such Ifmits to natural possi- 

 bilities, and not lightly accept theories which lead to supine- 

 ness when we ought to be stimulated to exertion. Whilst 



^ ' British and Foreign Medico-Chirurgical Review,' 1853, vol. xi. 

 p. 175- 



