4 LIFE AND DEATH. 



doctrines have undergone more or less profound 

 modifications. The changes of form, which have been 

 made necessary by the acquisitions of contemporary 

 science, enable us to appreciate its progress. They 

 enable us to give an account of the progress of 

 biology, and for this reason they deserve to be 

 examined with some attention. It is into this 

 examination that I ask my readers to accompany me. 



