Vlll PREFACE. 



The chemical forces play a part in all the pro- 

 cesses of the living animal organism; and a 

 number of transformations and changes in the 

 living body are exclusively dependent on their 

 influence. The diseases incident to the period of 

 growth of man, contagion and contagious matters, 

 have their analogues in many chemical processes. 

 The investigation of the chemical connexion 

 subsisting between those actions proceeding in the 

 living body, and the transformations presented by 

 chemical compounds, has also been a subject of 

 my inquiries. A perfect exhaustion of this sub- 

 ject, so highly important to medicine, cannot be 

 expected without the co-operation of physiologists. 

 Hence I have merely brought forward the purely 

 chemical part of the inquiry, and hope to attract 

 attention to the subject. 



Since the time of the immortal author of the 

 " Agricultural Chemistry," no chemist has occu- 

 pied himself in studying the applications of che- 

 mical principles to the growth of vegetables, and 

 to organic processes. I have endeavoured to 

 follow the path marked out by Sir Humphry 

 Davy, who based his conclusions only on that 

 which was capable of inquiry and proof. This is 



