694 



SCIENCE 



[N. S. Vol. XXV. No. 644 



The Protozoa from the Standpoint of the 

 General Naturalist: Edmund B. Wilson. 

 The zoologist who is asked to open a dis- 

 cussion on pathogenic protozoa with a few 

 remarks on these animals as they appear 

 from the standpoint of the general nat- 

 uralist must approach his task with some- 

 what mixed feelings. There is hardly a 

 field in zoology more interesting or fuller 

 of suggestion; but neither has any other 

 been oftener traversed or more widely ex- 

 ploited. Indeed the subject has been so 

 often discussed, its importance is so well 

 understood, that I am tempted to begin 

 and end with the celebrated remark of 

 Colonel Ingham's double that "there has 

 been so much said, and on the whole so well 

 said, that I will not further occupy the 

 time." And yet there are certain aspects 

 of the subject to which one may again and 

 again return without loss of interest, which 

 are a perennial spring of new ideas and 

 new research. First and foremost among 

 these is the fundamental analogy pointed 

 out by Virchow and Haeckel between the 

 animal body and an organized social state. 

 The conception that the multicellular body 

 is a 'cell-state'— a community of coop- 

 erating elementary organisms that are indi- 

 vidually comparable to protozoa— made a 

 deep and lasting mark on all morphology, 

 physiology and pathology. Apparently 

 there is no end to the fruits that it has 

 produced, continues to yield, and seems 

 likely to bring forth hereafter. The con- 

 ception is no doubt an inadequate one. 

 There are some, perhaps many, biological 

 piocesses that can not adequately or profit- 

 ably be considered from this point of view 

 alone. Especially in the field of growth 

 and development there are processes that 

 are better treated as the action of a single 

 and indivisible physiological unit than as 

 a resultant of cooperating cell-activities. 

 But, whatever its limitation may be, the 



conception of the 'cell state' remains one of 

 the most brilliant, interesting and fruitful 

 of the fundamental generalizations of biol- 

 ogy. It is part of the air we breathe in 

 every biological laboratory from the day 

 we first sit down to the microscope, and in 

 one way or other it pervades the whole 

 tissue of our work. As such it needs no 

 analysis at my hands. 



But there are certain applications of this 

 conception to some of the broader questions 

 of our science on which for a moment I 

 may appropriately dwell. For instance, 

 our conception of heredity, on which the 

 whole modem theory of evolution turns, 

 has been profoundly affected by the phe- 

 nomena of reproduction in the protozoa; 

 and the same is true of the whole constella- 

 tion of problems relating to sexuality, the 

 duration of life, old age, and the renewal 

 of vitality by fertilization, all of which are 

 in close relation to the problems of hered- 

 ity. A great number of the modern re- 

 searches on these questions can be recog- 

 nized as fruits of the celebrated compari- 

 son, drawn by Biitschli thirty years ago, 

 between the life-cycle of a protozoan race 

 and that of a multicellular animal. Fer- 

 tilization of the egg is analogous to the con- 

 jugation of the protozoa ; cleavage and de- 

 velopment to the successive divisions of the 

 ex-con jugants and their descendants; ma- 

 turity, decline and old age in the multicel- 

 lular organism to the physiological balance 

 and the ensuing gradual failure of vitality 

 after prolonged vegetative reproduction in 

 the protozoa; the stimulus to development 

 given by fertilization is comparable to the 

 renewal of vitality that follows conjugation 

 in the protozoa. This comparison has di- 

 rectly or indirectly stimulated a multitude 

 of important and interesting researches on 

 the fertilization of the egg, on artificial 

 parthenogenesis, on the chemical renewal 

 of vitality in the protozoa, on the stages of 



