Life and Protoplasm - 15 



cial trainings are rooted in a sound concep- 

 tion of general principles, the practitioner 

 lacks a background for critical judgment and 

 proceeds by rule of thumb. Likewise in many 

 other fields — in forestry, agriculture, and 

 horticulture; in animal and plant breeding; in 

 veterinary medicine and in the work of the 

 fisheries— biology has great practical value. 



Above and beyond the practical uses of 

 biology, however, there lies an even more im- 

 portant realm of values — the contributions of 

 biological sciences to human thinking and 

 philosophy. All of science provides a chal- 

 lenge to man's intellect, but the ideas of bio- 

 logical sciences have a uniquely direct bear- 

 ing upon our concepts of origin and destiny, 

 and upon how that destiny may be guided 

 and achieved. 



Continuity of Life. Nonliving matter is con- 

 tinually converted into living matter by con- 

 structive metabolism; and living matter is 

 continually reconverted into lifeless matter 

 by destructive metabolism and by the death 

 of organisms. But so far as we know, non- 

 living matter is converted into living matter 

 only in intimate association with existing 

 protoplasm — that is, in living organisms. In 

 this present geological age, living organisms 

 are known to originate only from other liv- 

 ing organisms, by the processes of reproduc- 

 tion. It seems logically inevitable that living 

 matter must have originated, in the remote 

 past, from nonliving matter, without the in- 

 tervention of previously living matter, but 

 the evidence as to how and under what condi- 

 tions this happened, is rather scanty. 



TEST QUESTIONS 



1. Specify the activities that are generally ex- 

 hibited by living things. To what extent are 

 these activities limited to living things? 



2. Explain in what manner the "growth" of a 

 crystal differs from the growth of typical liv- 

 ing bodies. 



3. Name three viruses and explain how the sim- 

 plest viruses differ structurally from small liv- 

 ing organisms such as bacteria. 



4. Why is it necessary to reserve judgment in 

 deciding whether the viruses are alive? Ex- 

 plain carefully. 



5. Explain why control experiments are very im- 



portant, exemplifying the discussion by a spe- 

 cific example. 



6. Differentiate among hypothesis, theory, and 

 principle, using specific examples. 



7. Explain why hypotheses are important in sci- 

 entific research. 



8. Give a careful definition for each of the fol- 

 lowing terms: (a) life; (b) protoplasm; (c) 

 biology; (d) nutrition; (e) responsiveness; (f) 

 reproduction; (g) metabolism; (h) ultramicro- 

 scopic structure. 



9. What is the basis of the statement that "proto- 

 plasm displays an unstable structure"? 



FURTHER READINGS 



1. The Virus: Life's Enemy, by K. M. Smith; tion of articles from Scientific American; New 

 New York, 1948. York, 1955. 



2. The Physics and Chemistry of Life, a collec- 3. Science and Common Sense, by J. B. Conant; 



New Haven, 1951. 



