Xll PREFACE. 



No one will venture to maintain, that the know- 

 ledge of the forms and of the phenomena of motion 

 in organized beings is either unnecessary or unprofit- 

 able. On the contrary, this knowledge must be 

 considered as altogether indispensable to that of the 

 vital processes. But it embraces only one class of 

 the conditions necessary for the acquisition of that 

 knowledge, and is not of itself sufficient to enable 

 us to attain it. 



The study of the uses and functions of the diffe- 

 rent organs, and of their mutual connection in the 

 animal body, was formerly the chief object of physi- 

 ological researches ; but lately this study has fallen 

 into the back-ground. The greater part of all the 

 modern discoveries has served to enrich comparative 

 anatomy far more than physiology. 



These researches have yielded the most valuable 

 results in relation to the recognition of the dissimi- 

 lar foiTns and conditions to be found in the healthy 

 and in the diseased organism ; but they have 

 yielded no conclusions calculated to give us a more 

 profound insight into the essence of the vital pro- 

 cesses. 



The most exact anatomical knowledge of the 

 structure of the tissues cannot teach us their uses ; 

 and from the microscopical examination of the most 

 minute reticulations of the vessels we can learn no 



