clii THE BEGINNINGS OF LIFE. 



' It has been a matter of common observation from the earliest 

 times, and our history will testify to its accuracy, that wide- 

 spread pestilence in plants, and murrain in animals, have 

 frequently either preceded, accompanied, or followed closely 

 on those visitations which caused mortality and mourning in 

 the habitations of men ; showing an identity of causation or 

 affinity which strongly tempts the inquirer to solve the secret 

 of their joint production V * Causes ' of this kind, however 

 obscure, are undoubtedly none the less real. Whilst we 

 may hope, therefore, that increasing knowledge will ultimately 

 enable us to throw more light upon their nature, we may at 

 least feel assured that the efficacy of these ' causes ' may be 

 increased or diminished by us at will. ' Exciting ' causes of 

 all ordinary severity require to be supplemented by the action 

 of 'predisposing' causes existing in the individual himself 

 before disease can be generated. It is true that we are com- 

 paratively powerless to rectify mere individual idiosyncrasies, 

 of the very nature and existence of which we may be ignorant, 

 but they constitute a mere fractional part of the predisposing 

 causes which favour the spread of epidemic affections. 

 These are, in the main, produced in the individual by 

 the operation of the more general exciting causes of 

 disease, such as bad or insufficient food, bad water, and im- 

 pure air ; or they are dependent upon more special causes, 

 such as depressing emotions, excessive muscular exercise, 

 or the occurrence of any unusual amount of degenerative 



1 If additional reasons were needed to enforce the vast importance of 

 the fullest knowledge concerning these diseases, they are not wanting. 

 The same author writes : ' The losses from only two exotic bovine 

 maladies ("contagious pleuropneumonia," and the so-called '''foot-and- 

 mouth disease ") have been estimated to amount, during the thirty 

 years that have elapsed since our ports were thrown open to foreign 

 cattle, to 5,549,780 head, roughly valued at 83,616,834. The late in- 

 vasion of " cattle plague," which was suppressed within two years of its 

 introduction, has been calculated to have caused a money loss of from 

 five to eight millions of p mnds.' 



