456 MODERN CHEMISTRY. 



essential to life in its every part. The food we take hardly 

 enters the stomach before it becomes the subject of chemical 

 actions, which are continued and multiplied, till its final 

 assimilation and admission into the mass of circulating fluids. 

 All the secretions and excretions from the blood, many of 

 them singularly complex in nature, depend on like agency ; 

 subordinate, however, as is all besides in the animal frame, 

 to that vital action which we everywhere see in its effects, 

 though unable to separate or define it. Morbid changes and 

 growths may frequently be referred to the same actions, 

 abnormal in kind ; and we have cause to believe that, under 

 deficient vitality, either from disease or old age, these purely 

 physical processes do often so usurp upon the fabric and 

 functions of life as to become the immediate causes of death. 

 Equally may we believe, from recent researches in physi- 

 ology and pathology, that certain diseases have their origin 

 in chemical changes of the blood ; either generating morbid 

 agents within itself, or multiplying, by an action analo- 

 gous to fermentation, poisons and morbid matters received 

 into the body. This wonderful fluid, ever in motion and 

 change, and subject at once to chemical laws and to the 

 principle of life, is in itself a mine of future discovery ; not to 

 be worked otherwise than by consummate skill and perse- 

 verance, but well meriting the application of both. 



We have spoken of actions analogous to fermentation ; 

 and are thence led to notice shortly another great attainment 

 of Organic Chemistry in regard to the remarkable process so 

 named, and the kindred changes of putrefaction and decay. 

 All these depend on chemical decomposition, as it occurs in 

 organic compounds, and especially in those of which nitrogen 

 is a principal constituent. They make provision for that 

 constant succession in plants and animals, which is the con- 

 dition of organised existence on the earth. Carbonic acid, 

 ammonia, and water are supplied by the atmosphere as the 



