CHAPTER X 

 THE GENERAL PHYSIOLOGY OF THE PROTOZOA 



THE Protozoa, as has been seen in the previous chapters, exhibit a 

 wide range of structural differentiation, from forms which exemplify 

 a cell reduced to its simplest essential parts, nucleus and cytoplasm, 

 to others in which the cytoplasmic elements give rise in different 

 parts of the body to a great variety of structures and organs, each 

 subservient to some special function. In the Protozoa of simplest 

 structure, therefore, the study of the physiological activities of the 

 organism coincides, more or less, with that of the elementary 

 properties of the living substance, protoplasm, its peculiar powers 

 of metabolism and transmutation of energy ; while in Protozoa of 

 complicated organization the mechanism and mode of action of the 

 various cell-organs must be considered in relation to their structure, 

 so far as it can be made out. 



It is not possible to discuss adequately, in the limited space of a 

 chapter, the intricate problems, for the most part still very obscure, 

 of the vital mechanisms of elementary organisms. The matter can 

 only be dealt with here on broad general lines, and those desirous 

 of studying the subject further must consult the references given to 

 special works or memoirs.* On the other hand, the special functions 

 and mechanisms of the various cell-organs (" organellae") have been 

 considered in describing the structure of the organs themselves. 

 In this chapter, therefore, it is intended rather to fill the gaps left 

 in previous chapters ; and the physiological problems presented by 

 the Protozoa will be sketched in brief outline under the following 

 headings : (1) Nutrition and Assimilation ; (2) Respiration ; (3) Secre- 

 tion and Excretion ; (4) Transmutation of Energy ; (5) Reactions to 

 Stimuli and to Changes of Medium or Environment ; (6) Degenera- 

 tion and Regeneration. 



* For works dealing with the physiology of Protozoa in a general way the student 

 should consult especially Verworn, " Allgemeine Physiologic," Jena, 1907 (a trans- 

 lation of the second German edition, under the title " General Physiology," was 

 published by Macmillan, 1899) ; Prowazek, " Einfiihrung in die Physiologic dor 

 Einzelligen," Leipzig (Teubner), 1910 ; the chapter on the general physiology of 

 the Protozoa in Doflein's " Lehrbuch der Protozoenkunde " ; and the excellent 

 summary of methods and results of physiological investigations upon Protozoa 

 given by Putter in Tigersteclt's " Handbuch der Physiologischen Methodik." 



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