The constitution of the individual patient at the moment of the physician's attention is the product of two factors, nature and nurture, or heredity and environment, or, as some one has facetiously expressed it, the devil and circumstance. Some may wish to limit the definition of constitution to the consequences of heredity alone; but heredity acts in an environment to which the individual is both susceptible and responsive. Ancestry determines the substrate but environment continuously influences this historical product of the race and is jointly responsible for its momentary status.
The reader of Professor Holmes's judicial and lucid presentation of the respective fields of influence of these two biologic factors which determine human nature will soon detect the author's profound belief in the potency of heredity and, as he reads, will find the increment of the evidence for this more and more convincing. However, he will also find that at