CHAPTER TWO 



EXPERIMENTATION 



" The experiment serves two purposes, often independent 

 one from the other: it allows the observation of new facts, 

 hitherto either unsuspected, or not yet well defined; and it 

 determines whether a working hypothesis fits the world of 

 observable facts." — Rene J. Dubos. 



Biological experiments 



SCIENCE as we know it to-day may be said to date from the 

 introduction of the experimental method during the 

 Renaissance. Nevertheless, important as experimentation is in 

 most branches of science, it is not appropriate to all types of 

 research. It is not used, for instance, in descriptive biology, 

 observational ecology or in most forms of clinical research in 

 medicine. However, investigations of this latter type make use 

 of many of the same principles. The main difference is that 

 hypotheses are tested by the collection of information from 

 phenomena which occur naturally instead of those that are 

 made to take place under experimental conditions. In writing 

 the last part of the previous chapter and the first part of this 

 one I have had in mind the experimentalist, but there may be 

 some points of interest in these also for the purely observational 

 investigator. 



An experiment usually consists in making an event occur under 

 known conditions where as many extraneous influences as possible 

 are eliminated and close observation is possible so that relation- 

 ships between phenomena can be revealed. 



The " controlled experiment " is one of the most important 

 concepts in biological experimentation. In this there are two 

 or more similar groups (identical except for the inherent vari- 

 ability of all biological material); one, the "control" group, is 

 held as a standard for comparison, while the other, the " test " 

 group, is subjected to some procedure whose effect one wishes to 



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