INTR OD UCTION. 2 5 



fashioned into larger secondary units each of which is a definite aggregate of 

 chemical molecules and possesses certain properties or reactions that depend 

 upon the mode of arrangement. The idea is similar to that advanced by 

 mineralogists to explain the structure of crystals. They suppose that the 

 chemical molecules are arranged in larger or smaller groups to which the 

 name "physical molecules" has been given. So in living protoplasm it may 

 be that the smallest particles capable of exhibiting the essential properties 

 of life are groups of ultimate molecules, in the chemical sense, having a 

 definite arrangement and definite physical properties. These secondary units 

 of structure have been designated by various names such as " physiological 

 molecules," 1 "somacules," 2 micellae, 3 etc. Many facts, especially from the 

 side of plant physiology, teach us that the physical constitution of protoplasm 

 is probably of great importance in understanding its reaction to its environ- 

 ment. Microscopic analysis is insufficient to reveal the existence or character 

 of these " physiological molecules," but it has abundantly shown that proto- 

 plasm has always a certain physical construction and is not merely a struc- 

 tureless fluid or semi-fluid mass. 



What has been said above may serve at least to indicate the prevalent 

 physiological belief that the phenomena shown by living matter are in the 

 11 i;i in the result of the action of the known forms of energy through a substance 

 of a complex and unstable structure which possesses, moreover, a physical 

 organization responsible for some of the peculiarities exhibited. In other 

 words, the phenomena of life are referred to the physical and chemical struc- 

 ture of protoplasm and maybe explained under the general physical and 

 chemical laws which control the processes of inanimate nature. Just as in 

 the case of dead organic or inorganic substances we attempt to explain the 

 differences in properties between two substances by reference to the difference 

 in chemical and physical structure between the two, so with regard to living 

 matter the peculiar differences in properties that separate them from dead 

 matter, or for that matter the differences that distinguish one form of living- 

 matter from another, must eventually depend upon the nature of the under- 

 lying physical and chemical structure. 



In the early part of this century many prominent physiologists were still 

 so overwhelmed with the lnvsteriousness of life that they took refuge in the 

 hypothesis of a vital force or principle of life. By this term was meant a 

 something of an unknown nature that controlled all the phenomena ex- 

 hibited by living things. Even ordinary chemical compounds of a so-called 

 organic nature were supposed to be formed under the influence of this force, 

 and it was thought could not be produced otherwise. The error of this latter 

 view has been demonstrated conclusively within recent years : many of the 

 substances formed by the processes of plant and animal life are now easily 

 produced within the laboratory by comparatively simple synthetic methods. 



1 Meltzer : " Ueber die fundamentale Bedeutung der Erechiitterung fur die lebende Ma- 

 terie," Zeitschrift fur Biologie, Bd. xxx., 1894. 



-Foster: Physiology (Introduction). s NSgeli: Theorieder Oahrung, Miinchen, 1879. 



