10 NATIONAL TRENDS IN BIOLOGY 



sands of things which must be considered if all the facts 

 are to be known, yet which never can be known, because 

 of the limitations of the human senses and the human 

 intellect. 



Professor William Wundt, the first man in the world 

 to open a psychological laboratory, came to the conclu- 

 sion that "animals never think and humans but seldom." 

 This conclusion was drawn from experiments akin to the 

 following : 



If we put a glass tube into the duct from the parotid 

 gland of a dog (this is the gland which swells when one 

 has mumps ; it also pours out the secretion which makes 

 the "mouth water"), we can count the number of drops 

 of secretion which come forth normally in a given time. 

 If we now allow the animal to smell a piece of meat, the 

 secretion comes forth in the same manner but with in- 

 creased rapidity. Suppose, then, we take a small amount 

 of hydrochloric acid and place it under the tongue. The 

 secretion increases to the same rate as it did when the 

 dog smelled meat. If, now, we blow a whistle some twenty 

 times at the precise moment the acid is placed under the 

 tongue, thereafter we only need to blow the whistle to 

 obtain the same result. The association of whistle and 

 acid has become so strong and so thoroughly connected 

 that one has the same effect as the other. But if the tone 

 of the whistle is changed, the same result will not be 

 produced. 



Such experiments prove that even so complicated and 



