,* ■^.' 



SPECIES LIVING TODAY DIFFER FROM THOSE OF THE PAST 



Just as there are many kinds of bears or bananas living today, the fossils show us 

 that there were in the past many kinds of plant and animals which strongly resembled 

 present-day species, yet differed from them in many ways 



energy becomes muscular action. It is true tiiat lifeless matter is transformed 

 into starch and into muscular action only by existing organisms. But in the 

 course of a century chemists have been converting such lifeless matter into 

 more and more complex carbon compounds and nitrogen compounds of kinds 

 that have not been found in nature except as' parts of plants and animals (see 

 page 99). Lately chemists have made synthetically compounds related to 

 proteins and have even duplicated compounds of the vitamin and hormone 



type. 



In recent times chemists have shown that under certain conditions of tem- 

 perature and light and dilution, some of the simpler "organic" molecules 

 arise "spontaneously". These conditions set up in the laboratory are prob- 

 ably like those that existed ages ago before there were any organisms, when the 

 oceans were warmer and less salty than at present. These facts make it seem 

 reasonable to suppose that there first appeared various molecules of sugars and 

 proteins and fats — substances that are basic in protoplasm. Such compounds 

 by themselves are not, of course, Hving. Yet combinations of such compounds 

 behave in ways that suggest "life". 



These findings of biochemists support the hypothesis that compounds, 

 becoming more and more complex, lead in time to mixtures and combinations 

 that approach the living. We cannot say that life arises spontaneously at a 

 particular time. But it is reasonable to think that over a long period life 

 evolved out of forms of matter which had not existed in earlier stages of the 

 earth's history. 



Between Living and Nonliving On the basis of his "germ theory" of 

 communicable, or infectious, diseases, Pasteur managed the dramatic cure of 

 Httle Joseph Meister, bitten by a mad dog. He was unable, however, to find 

 the "germ" of rabies, and concluded that it was too small to be seen with any 

 microscope. Later it was found that this virulent or poisonous something 

 would pass through the pores of a clay or porcelain filter, which are too small 

 to let the smallest visible particles pass through. By the end of the century a 

 number of "filterable viruses" were known to cause infectious diseases. In 



444 



