484 



been applied in vital processes ; and although it would appear 

 at first sight almost incredible, we can now state positively to 

 a few grains weight how much tissue is decomposed in a 

 given time, and how much of the various kinds of food is 

 required to restore it. With this amount of knowledge of 

 the causes which pertain to the healthy existence of animal 

 life, we have been led to investigate, and ultimately to com- 

 prehend, others of a more complex nature which influence 

 its existence. The action of various foreign ingredients in 

 the system, like the application of re-agents in analysis, were 

 found to exercise a certain influence on the various com- 

 pounds in the system, and to modify the changes on which a 

 healthy action mainly depend. It is true that the action of 

 many substances still remains a mystery; but from having 

 perfectly made out the modus operandi of some, we may hope 

 soon to discover that of the rest. The chemical change of 

 organized tissue by the action of a corrosive poison, the 

 chemical action of ammonia, alcohol, and other stimulants, 

 and the influence of many organic salts, are all traceable to 

 certain well-known affinities which these matters possess for 

 certain substances with which they come in contact — affinities 

 which we can demonstrate in our ordinary chemical opera- 

 tions, as well as prove to exist in the body. It is from facts 

 and deductions such as these that I shall endeavour to trace 

 out the cause of the apparently mysterious operations of 

 malaria on the animal frame. 



The existence of epidemic or infectious diseases in any 

 locality — of a certain kind of fever, for instance, in places 

 surrounded with cesspools, stagnant drains, or putrid marshes; 

 of agues in damp undrained districts ; or of cholera in filthy 

 ill-ventilated dwellings — is of itself a sufficient proof that 

 something is generated there capable of disturbing the ordi- 

 nary healthy performance of some of the vital functions ; and 

 in endeavouring to discover this substance and to describe its 



