24 GENERAL BIOLOGY 



reap destruction ; forgetting that to obtain the truth in anything, all the 

 facts must be known and a valid interpretation placed upon the facts, 

 and this can only be done by considering man in his entirety in his 

 physical, mental, and ethical aspects. 



One must therefore weight life's dice with knowledge if correct- 

 ness is to be formed in any walk of life. 



Nearly every parent desirous of his child's welfare, wishes he could 

 leave the child the benefit of his own experience, so that the child could 

 profit by his parent's mistakes and not make the same ones. The value 

 of this may be appreciated when it is remembered that if this cannot 

 be done, there is absolutely no progress. For, each individual, instead 

 of starting where his parents left off and continuing onward, would 

 necessarily have to begin where they began, and, consequently, when 

 life came to a close they would be exactly where their parents had been 

 at the same time. 



Men of the past have therefore written their experience in books, 

 and we of to-day can profit not only by the experience of our immediate 

 parents but by the experience of all our forefathers. 



The laboratory has gone even a little further than this. 



As no one man could w r ork out every detail in the study of a single 

 plant or animal without having to take the work of all those into con- 

 sideration who had gone before and who had contributed something to 

 the knowledge of the particular plant or animal under discussion, so, 

 men have gathered into a single grouping the important physical experi- 

 ences which have been found convincing to their minds and have called 

 such grouping a textbook. 



The study of the subject-matter of such textbook, plus the actual 

 working out of these same convincing experiences (now called experi- 

 ments) in the laboratory, cause the student actually to see the way in 

 which proof is obtained for the various conclusions men hold. 



In fact, laboratory work, plus a study of the text, is the fulfillment of 

 the parent's wish that his child inherit the parent's experience. 



From the experiment which thus gives us conclusive evidence of the 

 way some physical process works, we draw our principles. 



Principles are mental tools without which no mental progress would 

 be possible. 



In fact, a principle is a law of nature, proved by physical experi- 

 ment, to which no exception has been found. Physics presents an 

 excellent illustration of the value of principles.* 



Everyone knows that if a substance, such as iron, which is heavier 

 than water, is placed in water it will sink. Yet iron ships do not sink. 



*An old Greek named Archimedes, while taking a bath, discovered that when he immersed his 

 body in a tub filled with water, his body lost considerable weight. Later he was able to prove 

 experimentally that the weight of the water that ran over the top of the tub was exactly the same 

 as the weight his body lost while immersed. It was this discovery which made iron ships possible. 



