14 GENERAL CONSIDERATIONS 



ing conjugation the macronucleus disintegrates, and that the parts which 

 Balbiani had considered eggs are resorbed in the protoplasm, the whole 

 nucleus being replaced by one of the subdivisions of the Nebenkern 

 (micronucleus). Butschli's interpretation of the process of conjugation 

 was equally happy. After observing that continued asexual division of 

 certain forms resulted in decreased size and a general "lowering of the 

 life energy," he concluded that the function of conjugation is to bring 

 about a rejuvenescence {Verjungung) of the participants (see Turner, 

 infra, Chapter XII). 



In the same year Engelmann (1876) obtained very similar results. 

 Quite independently of Biitschli he proved the error of Balbiani's view, 

 and came to the conclusion not far different from Biitschli's: "The con- 

 jugation of the Infusoria," he said, "does not lead to reproduction 

 through eggs, embryonic spheres, or any other kind of germ, but to a 

 peculiar developmental process of the conjugating individuals which 

 may be designated Reorganization {loc. cit., p. 628). 



The Use of Cultures 



Toward the end of the last century new methods of studying Pro- 

 tozoa gradually evolved; at first structures, or morphological considera- 

 tions were predominant; then the uses of these structures led to a general 

 treatment of physiology, and a vast literature on the functions of differ- 

 ent parts of Protozoa grew up. All of this, in the main, was founded 

 upon observations and little was done in the experimental field of proto- 

 zoan research. Staining technique aided, and great strides were made 

 in knowledge of the microchemistry of all classes of Protozoa. Variations 

 in structures and in functional activities became apparent, and the con- 

 ception of the life cycle, first definitely outlined by Schaudinn (1900) 

 as a series of forms and activities consecutively produced and performed, 

 was recognized as characteristic of every species (see Kofoid, infra, 

 Chapter XI). The larger fields of study thus inaugurated have become 

 the starting point for many lines of research, and the single individual 

 has long since ceased to be the most important goal in study of Protozoa. 



Any work on the life history, or portion of it, begins with observa- 

 tions on food and feeding habits of the protozoon in question. Experi- 

 ments must first be undertaken to find a suitable culture medium upon 



