284 PROGRESS OF SCIENCE IN THE CENTURY. 



In these various ways the living body may be 

 studied, and no one of them has been disregarded by 

 the physiologists. It is plain, however, that along 

 some of these lines at least no secure progress could 

 be made until the sciences on which physiological 

 investigations depend had begun to gain clearness 

 and stability. There could be no chemical physiol- 

 ogy when combustion was not understood, and little 

 physical physiology when heat was regarded as an 

 element or as an entity. It follows that almost all 

 analytic physiology involving chemistry and physics 

 must be comparatively modern, and that we are not 

 likely to find much value in the physiology of the 

 eighteenth century or earlier except in so far as that 

 was concerned with descriptions of the habits of the 

 intact creature, with observations on the gross func- 

 tions of organs, or with merely mechanical analysis. 



Sketch of Physiological Progress. In what are 

 called the Middle Ages (to which, as regards biology 

 and psychology, many people still belong) the an- 

 alysis of the organism was only incipient. Compara- 

 tive anatomy and comparative physiology were still 

 embryonic. Chemistry and Physics were not yet suf- 

 ficiently stable themselves to be able to help another 

 science to a firm foothold. Yet then, as ever, men 

 looked out upon nature with inquisitive eyes, accum- 

 ulated a wealth of sense-impressions, and recorded 

 their perceptions in more or less orderly form. 

 Many interesting phenomena of plant and animal life 

 were observed, and sometimes accurately described. 

 But when the medieval observers went beyond 

 this, and took the more characteristically scientific 

 step of devising general formula? for the sequences 

 and likenesses which they perceived, they were al- 

 most forced to do so in metaphysical terms. Their 



