76 



LIFE S BEGINNING ON THE EARTH 



All these viruses can be killed or rather inactivated by 

 the same poisons that inactivate bacteria. Like other 

 living things, they have a remarkable propensity for chang- 

 ing into different types. 



/ 



Fig. 28. Crystalline Protein from Tobacco Mosaic 



Crystals indicate chemical purity. The chemically pure substance of 

 these crystals is at the same time a living entity. Magnified 400 times. 

 (From W. M. Stanley, Isolation and Properties of Virus Proteins in Ergeb- 

 nisse der Physiologie, biologischen Che.mie, und experirnentcllen Pharma- 

 kologie, volume 39.) 



m& 



V .* 





Fig. 29. Diseased Spots on Leaves op a Species of Tobacco Caused by 

 Solutions of Different Strengths of the Virus Protein 



(From W. M. Stanley as cited before) 



8 



LIFE AS THE PROPERTY OF A HIGHLY SPECIALIZED KIND 



OF MATTER 



Life is thus a properly of certain types of matter. Which 

 materials, we may ask, can be considered alive? Evidently 



