PREFACE. 



Protozoology as a branch of the biological sciences, has meant 

 little more than the application of biological or zoological methods 

 to a definite but limited group of organisms, the Protozoa. The 

 taxonomical, morphological and cytological aspects are well devel- 

 oped, and much progress has been made on the pathological side as 

 well as on the side of general physiology, distribution and ecology. 

 But there is no common aim, little common background and no 

 common point of view through which these many aspects of Pro- 

 tozoa-study are woven together in any definite way to make a 

 science of Protozoology. In this respect Protozoology differs 

 from other branches of the Biological sciences. Bacteriology, for 

 example, deals with miscellaneous minute organisms, but the science 

 is well-knit through special technical methods and by serological 

 aims. Genetics has for material the whole world of living things, 

 but is more definite in its ends than almost any other branch of the 

 biological sciences. 



Knowledge concerning the Protozoa has developed upon one 

 fundamental concept, viz.: that they are organisms of one cell. 

 This, however, has not been a unifying conception; indeed, through 

 sophistry, even this common ground is questioned by some. As a 

 student of the Protozoa for many years, and as a teacher, it seems 

 to me that what is most needed in protozoology at the present time 

 is a common point of view from which we may compare and evaluate 

 the vast annual output of observations and experiments. For 

 such a common viewpoint it is necessary, however, to go beyond 

 the conception of the cell to the underlying and more fundamental 

 principles of biology. 



In the present work I have brought together the conclusions 

 founded on thirty years of research on the Protozoa and on an equal 

 number of years of teaching protozoology at Columbia University 

 and recently at the Marine Biological Laboratory at Woods Hole. 

 I venture to hope that the presentation may be a step towards the 

 unification of the various phases of Protozoa-study and a suggestion 

 of a common point of view in protozoology. 



The underlying biological principle in this presentation is the 

 irritability of protoplasm, combined with protoplasmic organization. 

 This organization is specific for each type of living things and is 



