INTRODUCTION. 95 



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

 molecules/ 71 " somacules," 2 micellse, 3 etc. Many facts, especially from" tin- 

 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. Most interesting in this connection are tin- 

 recent views of Biitschli, 4 who believes that protoplasm is an aggregation of 

 fluid vesicles filled with fluid, resembling somewhat the structure of a foam 

 or the oily vesicles of an emulsion. He has in fact constructed an artificial 

 foam of oil and potassium carbonate which not only gives many of the micro- 

 scopic characters of protoplasm, but simulates the movements and currents 

 observed in lower forms of life. 



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 

 main the result of the action of the known forms of energy upon 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 may be 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 which separate them from dead 

 matter, or for that matter the differences which 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 mysteriousness 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 which 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. 

 By the distinguished labors of Emil Fischer 5 even the structure of carbohy- 



1 Meltzer : " Ueber die fundamentale Bedeutung der Erschutterung fiir die lebende Ma- 

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



2 Foster : Physiology (Introduction). 3 Nageli : Theorie der Gahrung, Munch. 



* Investigations on Microscopic Foams and on Protoplasm, London, 1894; abstracted 

 N. S., vol. ii. No. 52, 1895. 



5 Die Chemie der Kohlenhydrate, Berlin, 1894. 



