66 THE TREND OF THE RACE 
agencies on embryonic development is the great variety of anom- 
alies which are produced in response to any one agency. Féré’s 
interest in the causation of innate defect led him to consider the 
problem of how development may be influenced by external 
factors, and accordingly we find the author of the Pathology of 
the Emotions and various other treatises on abnormal psychology 
and nervous disorders, writing numerous notes upon the effect of 
all sorts of agencies upon the development of the egg of the 
domestic fowl. Injurious agencies generally effect a retardation 
of development and the production of various anomalies; more 
rarely there are produced individuals defective in certain respects 
but presenting in general a superior development. 
There is a certain parallelism between the manifestations of 
morbid heredity and the pathological effects of injurious agencies. 
Just as certain substances produce a great variety of teratological 
effects in the developing embryo, so certain hereditary factors 
result in very diverse characters in the adult organism. The 
toxins of a chronic disease such as syphilis produce a bewildering 
multiplicity of symptoms, and it should occasion no surprise that 
certain inherited tendencies should do likewise. If there be 
hereditary factors whose effect on development is to produce a 
general retardation and deterioration after the manner of the 
toxic influence of some chemical substance, the manifestations of 
these factors in successive generations might take the form of 
stigmata of degenerations as varied as those which occur in many 
families of defective human beings. Féré speaks of such phenom- 
ena as indicative of ‘‘the dissolution of heredity,” as if we were 
dealing with something which weakened or broke up the force of 
embryogenic energy. Perhaps the germ plasm of certain individ- 
uals may contain elements which tend to destroy the fidelity of 
hereditary resemblance, although it may be questioned whether 
this would in strictness be a dissolution of heredity. 
It is, of course, possible to maintain that the multiplicity of 
degenerative phenomena in human beings is the result of various 
unit factors each of which tends to produce a particular kind of 
defect. However true this may be in regard to certain character- 
