SCIENCE 



Friday, August 5, 1921 



CONTENTS 

 Parasitism as a Factor in Disease : Db. Theo- 

 bald Smith 99 



The First Appearance of the True Mastodon 

 in America: Dr. Henry Fairfield Osborn. 108 



Scientific Events: 



The Science Club of the University of Mis- 

 sissippi; The Work of the Bocke feller Foun- 

 dation; The Exposition of Chemical Indus- 

 tries; The Chemical Meeting in New York 

 City 108 



Scientific Notes and News Ill 



and Educational News 113 



Discussion and Correspondence: 



A Defense of Professor Newcomb's Logic: 

 Dr. W. W. Campbell. Biological Control of 

 Destructive Insects: De. Paul Popenoe. 

 A Longlived Woodborer: H. E. Jaques. 113 



Quotations : 



The Cost of Printing Scientific Works in 



England 114 



I 

 Special Articles: 



A Bacterial Disease of Gladiolus: Lucia 



McCULLOCH 115 



The American Chemical Society: Dr. Charles 

 L. Parsons 116 



MSS. intended for "publication and books, etc., intended for 

 review ahould be sent to The Editor of Science, Garrison-on- 

 Hudson, N. Y. 



PARASITISM AS A FACTOR IN 

 DISEASE 1 



The study of etiology or causation is a 

 study of the entire field of medicine from a 

 certain point of view. Every phenomenon as- 

 sumes an etiological aspect vehenever we study 

 it not as an effect to be simply contemplated 

 and described, but as a cause or necessary con- 

 dition of something that is going to happen. 

 Provided with the informatiem that for cer- 

 tain events to take place certain necessary con- 

 ditions must precede, we can take steps by con- 

 trolling the necessary conditions to allow the 

 event to occur or not. Modern medicine has 

 made the concept of causation its own. On it 

 is founded all rational progress in prophylaxis 

 and therapy. First to comprehend the cause, 

 then to intercept and suppress it and thereby 

 to prevent the next step is the kernel of med- 

 ical science and practise. We project our- 

 selves into the immediate future. The present 

 is only the boundary between what has oc- 

 curred and what is to happen. To control 

 events we must know how to distinguish those 

 conditions which are necessary from those 

 which are merely associated and coincident. 



The history of medical science, notably dur- 

 ing the past half century, has clearly shown 

 that observation of disease as it occurs in 

 everyday life must be associated with the ex- 

 periment. By observation I mean a survey or 

 study of the phenomenon as a whole; by ex- 

 periment, the observation of isolated parts of 

 the entire phenomenon, the other parts being 

 meanwhile eliminated or controlled by special 

 devices. Observation and experiment, alter- 

 nating, cooperating, and reacting on each 

 other, are the only sure guides to a rational 

 interpretation of disease. Nature is continu- 



1 Paper read at the amiual meeting of the 

 Association of American Physicians, May 10, 1921, 

 as part of a sjTnposimn on etiology or causation 

 of infectious diseases. 



