Vi PREFACE 



discovery which has enabled us to look forward to a change in the direction of the 

 labours of physiologists. The time for such a change is now at hand ; and a per- 

 severance in the methods lately followed in physiology would now, from the want, 

 which must soon be felt, of fresh points of departure for researches, render phy- 

 siology more extensive, but neither more profound nor more solid. 



No one will venture to maintain that the knowledge of the forms and of the 

 phenomena of motion in organized beings is either unnecessary or unprofitable. 

 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 different organs, and of their mutual 

 connection in the animal body, was formerly the chief object of physiological re- 

 searches ; 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 recog- 

 nition of the dissimilar forms 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 processes. 



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 more as to their functions than we 

 have learned concerning vision from counting the surfaces on the eye of the fly. 

 The most beautiful and elevated problem for the human intellect, the discovery of 

 the laws of vitality, cannot be resolved, nay, cannot even be imagined, without an 

 accurate knowledge of chemical forces ; of those forces which do not act at sensi- 

 ble distances ; which are manifested in the same way as those ultimate causes by 

 which the vital phenomena are determined ; and which are invariably found active, 

 whenever dissimilar substances come into contact. 



Physiology, even in the present day, still endeavours, but always after the 

 fashion of the phlogistic chemis-ts (that is, by the qualitative method,) to apply 

 chemical experience to the removal of diseased conditions; but with all these 

 countless experiments we are not one step nearer to the causes and the essence of 

 disease. 



With proposing well-defined questions, experimenters have placed blood, urine, 

 and all the constituents of the healthy or diseased frame, in contact with acids, 

 alkalies, and all sorts of chemical re-agents ; and have drawn, from observation of 

 the changes thus produced, conclusions as to their behaviour in the body. 



By pursuing this method, useful remedies or modes of treatment might by acci- 

 dent be discovered ; but a rational physiology cannot be founded on mere re-actions, 

 and the living body cannot be viewed as a chemical laboratory. 



In certain diseased conditions, in which the blood acquires a viscid consistence, 

 this state cannot be permanently removed by a chemical action on the fluid circu- 

 lating in the blood-vessels. The deposit of a sediment from the urine may 

 perhaps, be prevented by alkalies, while their action has not the remotest tendency 

 to remove the cause of disease. Again, when we observe, in typhus, insoluble salts 

 of ammonia in the faeces, and a change in the globules of the blood similar to that 

 which may be artificially produced by ammonia, we are not, on that account, 



