GENERAL INTRODUCTION 6 



and animals as well organized cell federations was possi- 

 ble only after the existence and physiology of unicellular 

 beings had been established. Considering the very 

 little attention paid hitherto to the physiology of bacteria, 

 it seems quite possible that many new contributions to 

 general physiology might originate from the study of the 

 simplest forms of life. 



Most favorable to such studies is the attitude of 

 Putter in his book on Comparative Physiology (published 

 as early as 1911): 



"It might perhaps surprise many to find so much space given 

 to the discussion of the biochemistry of molds, yeasts and bacteria; 

 however, with just these organisms, a clear conception of the different 

 metabolic processes can be obtained, and the aim of a comparative 

 physiology seems to me to consist rather more in working out the 

 various principles with the organisms best suited for this purpose 

 than in enumerating a larger number of experiments from all the 

 groups of organisms existing." 



It is not conceivable that any scientist would con- 

 sider it possible to substitute physiological experiments 

 with the liver or the thyroid gland by experiments with 

 bacteria. Nor is it likely that anybody would believe 

 nutrition experiments with higher animals superfluous 

 and replaceable by experiments with lower fungi. The 

 very simplicity of the metabolism of some microorgan- 

 isms makes them fit for a good many experiments which 

 cannot be carried out with higher plants or animals. 

 That is why the physiology of microorganisms is of con- 

 siderable importance in general physiology. 



Some of the advantages of using microorganisms in 

 physiological experiments of a more general nature, are: 

 (1) the absolute control of temperature during the entire 

 experiment, and the possibility of working at several 

 different temperatures; (2) the absolute control of food 

 which may be chosen from chemically pure and well 



