APPENDIX I 



TERATOLOGICAL HEREDITY 



TitB peculiar mode of inheritance which is knoivn as teratologioal may 

 seem at iirst sight to contradict in certain respects the theory of the non- 

 transmission of somatic modifications. We are not aware that the subject 

 has been discussed, either in the works of Weismann or in those of his 

 followers. It may be useful, therefore, to devote a little space to a con- 

 sideration of the facts. Teratological inheritance involves the transmission 

 of certain structural malformations, and may be treated under the heading 

 of morphological pathology. 



It would be a mistake, however, to suppose that these pathological mal- 

 formations, which manifest themselves ia the body of the organism, and 

 are indubitably hereditary, are exdusivdy somatic. 



It is safe to say that such malformations, which often present the appear- 

 ance of an atavistic Tretum to an ancestral type, are never to be found 

 except on what the French call un terrain morbide. They are the somatic 

 expressions of an organic disease which affects the germ-plasm as much as 

 the soma. 



Illustrations of the transmission of teratological malformations are 

 numerous. We need only cite a few examples, as this is not a medical 

 treatise. The symmetrical atrophy of the parietal bone of the cranium 

 may be hereditary. The same may be said of anomalies in the develop- 

 ment of the arteries, the pathogenic results of which are well known. 

 The congenital narrowing of the pulmonary artery is a factor predisposing 

 to pulmonary tuberculosis. Atresia of the aorta has a considerable influ- 

 ence on the pathology of the heart ; chlorosis, that spontaneous anaemic 

 condition which manifests itself at puberty, is sure to develop on ground 

 which is well prepared by the abnormally small size of the heart. Aplasia 

 of the arteries, insufficient development of the uterus and ovaries, and 

 chlorosis, can be hereditary. Consumption is favoured by a number of 

 malformations of the thorax ; and all these abnormalities have the result 

 of diminishing the respiratory capacity of the patient, of exaggerating the 

 already insufficient activity of the upper part of the lung ; they therefore 

 predispose the patient to microbic infection. It is generally admitted 

 that patients suffering from thoracic malformations are more exposed than 

 others to bronchial pneumonia. The inheritance of appendicitis has been 



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