54 THE FOUNDATIONS OF ZOOLOGY 



far as it is joined to consciousness and volition and reason, it is 

 identical with the practical application of scientific knowledge. If 

 we were sure that all living things are conscious and endowed 

 with memory and volition, as they may be for all I know to the 

 contrary, we might define life as knowledge in use ; for the re- 

 sponsive actions of living things are such that our reason approves 

 them as judicious and beneficial. This truth has often found ex- 

 pression in the statement that living things use the properties of 

 the world around them for their own good or the good of their 

 species. 



The same thought may be expressed by the statement that 

 life is the use of the natural language of signs; for each stimulus 

 to a vital act is a sign with a significance; and the act is itself 

 a response to the significance of which, in course of nature, the 

 stimulus is a sign. 



To study life we must consider three things : first, the orderly 

 sequence of external nature ; second, the living organism and the 

 changes which take place in it ; and, third, that continuous adjust- 

 ment between the two sets of phenomena which constitutes life. 



The physical sciences deal with the external world, and in the 

 laboratory we study the structure and activities of organisms by 

 very similar methods ; but if we stop here, neglecting the rela- 

 tion of the living being to its environment, our study is not biology 

 or the science of life. Now, whatever its equivalent in the struct- 

 ure of organisms may be, the reality in our own minds behind 

 such words as use, fitness, and response, is not a phenomenon, 

 which can, in this century at least, be weighed or measured or 

 made manifest to sense, but a relation, apprehended by our think- 

 ing minds ; for beneficial response is one thing, and conscious 

 apprehension of the benefit of response quite another thing. Men 

 who know nothing of the sciences of optics and acoustics profit, 

 like philosophers, by seeing and. hearing; as do also the snail and 

 the jelly-fish, whether they know they have eyes and ears or not. 



While biology presents endless opportunities for the profita- 

 ble application of the methods of research which are employed 

 in physical science, it also brings before us a new problem, the 

 problem of fitness, which demands new methods of inquiry, and 

 is different from the physics and chemistry of the living body. 



