6 INTRODUCTORY. 



long-run we have to fall back upon the properties of carbon, 

 hydrogen, nitrogen, oxygen, etc., for the properties of living 

 matter. 



Scope of Biology. The Biological Sciences. It follows from 

 the broad definition given to Biology that this science includes 

 the study of whatever pertains to living matter or to living 

 things. It considers the forms, structures, and functions of living 

 things in health and in disease ; their habits, actions, modes of 

 nutrition ; their surroundings and distribution in space and time, 

 their relations to the lifeless world and to one another, their 

 sensations, mental processes, and social relations, their origin and 

 their fate, and many other topics. It includes both zoology and 

 botany, and deals with the phenomena of animal and vegetal life 

 not only separately, but in their relations to one another. It 

 includes the medical sciences and vegetal pathology. 



The Held covered by biology as thus understood is so wide as 

 to necessitate a subdivision of the subject into a number of principal 

 branches which are usually assigned the rank of distinct sciences. 

 These are arranged in a tabular view on p. 7. The table shows 

 two different ways of regarding the main subject, according as 

 the table is read from left to right or vice versa. Under the more 

 usual arrangement biology is primarily divided into zoology and 

 botany, according as animals or plants, respectively, form the 

 subject of study. Such a division has the great advantage of 

 practical convenience since, as a matter of fact, most biologists 

 devote their attention mainly either to plants alone or to animals 

 alone. From a scientific point of view, however, a better sub- 

 division is into Morphology (ywop0//, form" Aoyos, a discourse) 

 and Physiology ((fivcris, nature; Aoyos, a discourse). The 

 former is based upon the facts of form, structure, and arrange- 

 ment, and is essentially statical ; the latter upon those of action 

 or function, and is essentially dynamical. But morphology and 

 physiology are so intimately related that it is impossible to sepa- 

 rate either subject absolutely from the other. 



Besides the sub-sciences given in the table a distinct branch 

 called ^Etiology is often recognized, having for its object the in- 

 vestigation of the causes of biological phenomena. But the sci- 

 entific study of every phenomenon has for its ultimate object the 

 discovery of its cause. ^Etiology is therefore inseparable from 



