PROTOZOA AND OTHER ANIMALS 891 



obtaining nutriment from the living substance of the latter, depriving it 

 of useful substance, or exerting other harmful influence upon it. In the 

 interests of exactitude, a word should, if possible, express a single defi- 

 nite idea; and therefore it seems undesirable to use parasitism also in 

 a general sense if it can be avoided. 



There is much justification for applying the term symbiosis to the 

 general relationship under consideration, although many authors have 

 given it a restricted applicability to mutually advantageous associations 

 only. The word in this restricted meaning has, in fact, acquired what- 

 ever sanction general usage confers. Most textbooks in biology and 

 zoology, as well as protozoology and parasitology, so define it, the 

 oldest one noted being T. J. Parker's (1893); and Hegner (1926b) 

 restricted the meaning further, stating that in symbiosis life apart is 

 impossible. J. A. Thomson (1934; with Geddes, 1931; also in the 

 Encyclopaedia Britannica fourteenth ed.) contended that symbiosis 

 is a mutually beneficial internal relationship, and that externally mutual- 

 istic relationships are commensalism. To Haupt (1932) symbiosis 

 includes what others consider commensalism, but does not include 

 parasitism; the same sense is implicit in some dictionary definitions. 

 The extended meaning of the word has been found in only two general 

 biology texts (McFarland, 1913; Eikenberry and Waldron, 1930); 

 it has that meaning also in the article on symbiosis in the Neiv Interna- 

 tional Encyclopaedia (1925). Most important, however, is the report of 

 Hertig, Taliaferro, and B. Schwartz (1937). 



The sense in which the word was employed by its originator, A. de 

 Bary (1879), is of decisive importance. The three members of the 

 Committee on Terminology of the American Society of Parasitologists, 

 as well as W. Schwartz (1935), appear to have been the only ones 

 among recent authors to understand de Bary. It has been widely stated 

 that he meant symbiosis to designate mutually beneficial relationships 

 (by Caullery, 1922; Hegner, 1926b; as well as by the others cited in 

 the Committee's report). The Committee gave quotations from de 

 Bary showing clearly that he used symbiosis as a collective term, the 

 subdivisions of which include parasitism and mutualism; he recog- 

 nized two main categories, antagonistic and mutualistic symbiosis. The 

 results of the writer's examination of de Bary's paper are in complete 

 agreement with their interpretation; there is no ambiguity in de Bary's 



