96 ELEMENTAKY INSTRUCTION IN PHYSIOLOGY. 



who yet would vigorously object to give a verbal as- 

 sent to the doctrine itself. However this may be, the 

 main point is that sufficient knowledge has now been 

 acquired of vital phenomena, to justify the assertion, 

 that the notion, that there is anything exceptional about 

 these phenomena, receives not a particle of support from 

 any known fact. On the contrary, there is a vast and 

 an increasing mass of evidence that birth and death, 

 health and disease, are as much parts of the ordinary 

 stream of events as the rising and setting of the sun, 

 or the changes of the moon ; and that the living body 

 is a mechanism, the proper working of which we term 

 health ; its disturbance, disease ; its stoppage, death. 

 The activity of this mechanism is dependent upon many 

 and complicated conditions, some of which are hope- 

 lessly beyond our control, while others are readily ac- 

 cessible, and are capable of being indefinitely modified 

 by our own actions. The business of the hygienist and 

 of the physician is to know the range of these modifi- 

 able conditions, and how to influence them towards the 

 maintenance of health and the prolongation of life ; the 

 business of the general public is to give an intelligent 

 assent, and a ready obedience based upon that assent, to 

 the rules laid down for their guidance by such experts. 

 But an intelligent assent is an assent based upon knowl- 

 edge, and the knowledge which is here in question 

 means an acquaintance with the elements of physiology. 

 It is not difficult to acquire such knowledge. "What 

 is true, to a certain extent, of all the physical sciences, 



