OF VITAL ACTIONS IN GENERAL. VM 



ing the actions of the body when placed in different circumstances, from 

 which we judge of its properties, and of the forces to which these proper- 

 ties give rise when they are called into operation. 



24. It is hoped that the propriety of the distinct use of the terms 

 Vital Action, Vital Force, and Vital Property, will now be evident ; 

 and that the student will be prepared to attach distinct ideas to each_of 

 them. It is the business of the Physiologist to study those actions "or 

 phenomena, which are peculiar to living beings, and which are hence 

 termed vital : he endeavours to trace them to the operation of specific 

 forces acting through organized structures, just as the Astronomer 

 traces all the movements, regular and perturbed, of the heavenly bodies, 

 to the mutual attraction of their masses, acting concurrently with their 

 force of onward rectilinear movement ; or as the Chemist attributes the 

 different acts of combination or separation, which it is his province to 

 study, to the mutual affinities of the substances concerned : and the 

 physiologist, like the astronomer or the chemist, seeks to determine the 

 laws according to which these forces act, or, in other words, to express 

 the precise conditions under which they are called into play, and the 

 actions which they then produce. It is only in this manner, that Phy- 

 siology can be rightly studied and brought to the level of other sciences. 

 There can be no doubt that its progress has been greatly retarded by 

 the assumption, that its phenomena were all to be attributed to the 

 operation of some general controlling agency, or Vital Principle ; and 

 that the laws expressing the conditions of these phenomena, must be 

 sought for by methods of investigation entirely distinct from those 

 which are employed in other sciences. But a better spirit is now abroad; 

 and the student cannot be too strongly urged to discard any ideas of 

 this kind as absolutely untenable ; and to keep steadfastly in view, that 

 the laws of Vital Action are to be attained in the same manner as those 

 of Physics or Chemistry, that is, by the careful collection and com- 

 parison of vital phenomena, and by applying to them the same method 

 of reasoning, as that which is used in determining the forces and pro- 

 perties on which other phenomena depend. True it is, that we can 

 scarcely yet hope to reach the same degree of simplification, as that of 

 which other sciences are capable ; and this on account of the very com- 

 plex nature of the phenomena themselves, and the difficulty of satisfac- 

 torily determining their conditions. The uncertainty of the results of 

 Physiological experiments is almost proverbial : that uncertainty does 

 not result, however, from any want of fixity in the conditions under 

 which the vital forces operate, but merely from the influence of diffe- 

 rences in those conditions, apparently so slight as to elude observation, 

 and yet sufficiently powerful to produce an entire change in the result. 

 And, owing to that mutual dependence of the different actions of the orga- 

 nized structure, to which reference has been already made ( 5), we cannot 

 seriously derange one class of these actions, without also deranging, or 

 even suspending others : a circumstance which obviously renders vital 

 phenomena much more difficult of investigation than those of inorganic 

 matter. 



25. All sciences have their "ultimate facts ;" that is, facts for which 

 no other cause can be assigned than the Will of the Creator. Thus, in 



