MORBID HEREDITY. 395 



The want of resemblance in descent observed in pathological 

 and teratological families evidences the want of embryogenic 

 energy which is so accentuated in those families as to end in 

 sterility after a few generations. The attenuation of embryogenic 

 force which may be signalized by failures of very different ele- 

 ments may serve to interpret what is called dissimilar morbid 

 heredity and that paradoxical heredity designated as collateral 

 morbid heredity. 



It should be remarked that dissimilarity in morbid families is 

 not absolutely fortuitous. The head of a family gives rise to off- 

 spring suffering from different and differently seated disorders of 

 evolution, that cause various morbid predispositions, the variety 

 of which is, however, not so great but that we can find analogies in 

 the manifestation capable of giving a family resemblance to them. 

 Degeneration, in fact, does not take effect except under a kind of 

 rule. As Morel has well observed, unlike degenerates of one 

 family resemble unlike degenerates of another family to such an 

 extent that, like monsters, they are susceptible, wheresoever they 

 may come from, of a scientific classification. Degeneration has 

 its laws the same as normal evolution ; whatever may be its 

 cause, it is manifested under a relatively restricted number of 

 common forms. 



The theory of the teratological origin of manifestations of 

 morbid heredity is really the only one that will allow us to ex- 

 plain how very diverse conditions of generation, such as extreme 

 youth or too advanced age of progenitors, disproportion in their 

 ages, permanent or even transitory disorders in their vitality, 

 drunkenness, intoxications, infections, accidental exhaustion of the 

 nervous system, or acquired neurasthenia, can produce the same 

 effects as morbid heredity. We should not, in fact, be surprised 

 at finding that degenerates by heredity are not different from 

 degenerates in consequence of disorders of nutrition in progeni- 

 tors, since degeneration in general results from embryogenical 

 troubles which are reduced, as a whole, to troubles of nutrition. 

 The teratological theory of morbid heredity and of degeneration 

 permits us to comprehend not only unlikeness in morbid heredity, 

 but also the absence of heredity in diseases of the group pre- 

 sumed to be hereditary, but which might be more correctly called 

 degenerative. 



Greater importance attaches to disorders of development, 

 when we regard their consequences, as they are produced at a 

 period nearer the beginning of the evolution. External forms 

 are fixed long before the structure of the organs has reached per- 

 fection. Thus in man birth finds some parts of the nervous sys- 

 tem and the most important ones, when the light of relation is 

 regarded in full development. It is therefore easily compre- 



