PART I. METABOLISM 



LECTURE I 



INTRODUCTION 



Problems of Plant Physiology Methods Chemical composition 

 and structure of the plant. 



THE saying of the Greek philosopher iravra. pel ' everything is in a state 

 of flux,' is in the highest degree applicable to the living organism, for continuous 

 changes, both physical and chemical, are the inseparable characteristics of 

 life, not only in the organism as a whole, but in the individual parts of which 

 it is composed. Among these changes may be noted first those occurring in 

 the non-living body ; for instance, expansion as a result of exposure to increased 

 temperature is not limited to the inorganic world, and the living body as well 

 as the dead may be temporarily or permanently altered in form by mechanical 

 means. Purely physical or purely chemical changes, such as these, are of 

 but little interest to the physiologist, while, on the other hand, those changes 

 which are peculiar to the living organism, the possession of which differentiates 

 it from non-living nature, and which it no longer shows when life has passed 

 away from it, are of paramount physiological importance. To inquire into 

 the nature of such changes and, as far as may be, to trace them to their ultimate 

 physical and chemical causes are the special tasks of physiology. The ulti- 

 mate aim of the science, in a word, is not merely to attempt the elucidation 

 of the several changes individually, but also to arrive at a clear comprehension 

 of their relation to each other and, if it be possible, to solve the problem of 

 the nature of life itself. Neither in its general nor in its special aspect has 

 this goal as yet been reached. Whether it ever will be reached is a question 

 to which varied and equally dogmatic answers have been given, some optimistic, 

 some pessimistic, yet none of them can be said to be founded on any secure 

 basis of evidence. The attraction which science exerts on the mind of man 

 lies, however, not so much in the rapid attainment of the goal aimed at as 

 in the actual scientific inquiry itself, and that is the reason why those who cry 

 ' ignorabimus ' have not long ere this abandoned scientific research altogether. 



On inquiry we find that the changes which are characteristic of the living 

 organism are as follows : 



1. Much the most easily observed are the changes in form which every 

 organism exhibits during its life. From minute and for the most part 

 simple beginnings, each organism gradually increases in size in obedience to 

 certain recognized laws ; it increases in complexity also, or, in other words, 

 undergoes development, finally giving rise once more to the rudiments of a new 

 organism, which in its turn passes through a similar developmental history. 

 To these changes we shall give the name of Metamorphosis. 



2. Changes of position, or movement of the entire organism or of its 

 parts, are not readily observable in all forms. We shall find, however, that 

 all organisms do exhibit such movements, possible only in consequence of 



JOST B 



