WHAT IS PHYSICAL LIFE 



of life, not because it is a chemical poison, 

 but because it is a living growth belonging 

 to an infection historically known for cen- 

 turies. We cannot expect therefore that 

 / experimenters will soon be able artificially 

 to make life, when not only the yellow 

 fever agent, but those of hydrophobia, 

 rinderpest, and a number of other infec- 

 tions of cattle, are not large enough to be 

 seen by any microscope, and hence are 

 beyond handling. 



We have shown in the previous chapter 

 that Reproduction and Heredity are the 

 two fundamental factors in all physical 

 life, and how impossible it is to find any 

 analogue to them outside the domain of 

 life. But much the most striking illustra- 

 tions of both great reproductive powers 

 and of heredity are shown, for example, in 

 the case of the tubercle bacillus. His term 

 of life, instead of being, as with us, three- 

 score years and ten, is only from twenty 



