OTHER BRANCHES OF MEDICINE. 29 



velop themselves in the production of phenomena. These require to be 

 separately considered ; just in the same manner as when, in examining the 

 action of a steam-engine, we inquire into its mechanical structure, and the 

 effects upon it of the agencies by which it is put in operation. Now in the 

 study of Pathology, or the science of diseased action, we have to attend, in 

 the same manner, to two sets of conditions. On the one hand, we have to 

 make ourselves acquainted with the characters of all the external agents, 

 which can produce a deleterious effect upon the living body, whether their 

 operation be mechanical, chemical, or more directly vital ; as well as with the 

 results of the suspension, partial or complete, of the conditions by which its 

 healthy action is maintained. On the other side, we have to investigate the 

 changes of structure which manifest themselves in the body itself, the causes 

 by which these are produced, and the new results which they will themselves 

 occasion. Now one of the chief difficulties in the pursuit of Pathological 

 Science results from this, that we are at present so imperfectly acquainted 

 with the conditions required for normal action, that we cannot ascertain what 

 those changes are, in which the derangement primarily consists. Hence we 

 are in constant danger of mistaking the more evident changes, which are 

 often but secondary results of the morbid action, for the real source of the dis- 

 ease. For example, we are not yet sufficiently acquainted with the condi- 

 tions necessary for the transmission of nervous influence, to be able to state 

 when those conditions are interfered with ; hence a great extent of morbid 

 alteration not unfrequently presents itself, in the parts which we know to be 

 concerned in this operation, without such symptoms as we should expect to 

 correspond with it ; and, on the other hand, we frequently observe during life 

 most decided deviations from the ordinary sequence of nervous phenomena, 

 which we cannot attribute to any change of structure that we can discover 

 after death. Here, then, is a case in which Pathology must necessarily be 

 imperfect, until Physiology has greatly advanced ; and numbers of similar 

 instances might be pointed out. Again, it would be easy to show the direct 

 benefit which the Physician has derived from the Physiologist, by reference 

 to the same class of phenomena ; but for this we may refer to the subsequent 

 part of this Treatise, in which the chief practical applications of late discove- 

 ries as to the Functions of the Nervous System, will be set forth. It will be 

 scarcely questioned, then, that the Science of Pathology has so direct and 

 immediate a dependence upon that of Physiology, that the former cannot be 

 pursued with a fair prospect of success, without a knowledge both of the 

 principles and of the chief phenomena of the latter. 



9. Another illustration may be useful. Few Pathologists regard any mor- 

 bid process as better understood than that of Inflammation ; and yet scarcely 

 any two are agreed as to its real nature. By some, its essential condition is 

 stated to be a contraction or a dilatation of the capillary vessels; and this 

 alteration is supposed by one to result from an exalted and by another from 

 a diminished degree of vitality in their walls. Others, again, regarding 

 Inflammation as an affection of the sensory rather than of the organic func- 

 tions, have imagined its seat to be in the nervous system. Now it may be 

 stated with tolerable confidence, that no theoretical view of the nature of 

 Inflammation has exerted any beneficial influence on its treatment ; and that 

 all the rules of practice to which we trust for the cure, are founded on expe- 

 rience alone. It is therefore evident, that there must be something very faulty 

 in the mode of cultivation, since the fruits yielded by a domain so fertile of 

 phenomena are thus useless ; and the Physiologist has not much difficulty in 

 pointing out several sources of error thaf have resulted from the insufficient 

 acquaintance possessed by most Pathologists, with those normal actions of 

 which Inflammation is a disturbed form. Thus, he can show that Innamma- 



