This volume by one of the leading scientific men of America is one of great value and wide interest. We mention it here because much of its content has a bearing on Freud's later work, particularly his Beyond the Pleasure Principle. Those who remember the discussion in that book of the problem of somatic immortality will be interested to know that Professor Pearl, after carefully reviewing all the evidence, comes to the definite conclusion that uni-cellular organisms are immortal. The same is of course true of the germ cells of multi-cellular animals, and Carrel's recent work would seem to show that even somatic cells of multi-cellular organisms are in themselves immortal, losing this feature only through the complexity of life in the multi-cellular organism. The phenomenon of death is therefore in no sense inherent in vital organisms, but has made its appearance at a relatively late stage in evolution.

Of the many other interesting conclusions reached by Professor Pearl,