TRANSMISSION OF MICRO-ORGANISMS. 325 



the proof that actual morphological changes, such as modi- 

 fications of histological or molecular structure, can be trans- 

 mitted has not yet been given. It is conceivable that 

 predispositions may be inherited, and these must result 

 from alterations in the germ-plasm, or a direct infection of 

 the germ or embryo might cause the transference of a dis- 

 ease from one generation to another, a phenomenon which 

 simply depends upon a particular mode of conveyance of a 

 parasite. 1 



In many diseases, and particularly those which are directly 

 caused by micro-organisms, it is a matter of interest to note 

 the wide differences which exist between the conveyance 

 of hereditary characters, and of a specific disease. Armauer 

 Hansen (1) has made this perfectly clear in considering the 

 etiology of leprosy. He has pointed out that true heredi- 

 tary characters are usually limited to one sex, frequently 

 appear at a particular age, and the phenomenon of atavism 

 is not rare ; but in the conveyance of such a disease as 

 tuberculosis or leprosy, none of these conditions are ful- 

 filled. It is a logical deduction from the consideration of 

 these differences that every specific disease which is trans- 

 mitted cannot be regarded as hereditary, but as an instance 

 of the direct bacterial infection of the germ-cells or embryo. 

 Most writers on cancer and malignant growths have dis- 

 cussed the hereditary transmission of this disease, and if it 

 is allowed that a disposition to cancer may be derived by 

 inheritance, then this condition would depend upon some 

 peculiarity inherent in the nucleus of the germ-cells ; but 

 if, on the other hand, malignant disease is caused by a 

 parasite belonging, as some investigators have sought to 

 prove, to the group of protozoa or protophyta, then the 

 transmission of the actual disease will depend upon the 

 passage of a micro-organism which invades the germ or its 



1 " Pour les maladies, vraiement constitutionnelles, c'est la substance 

 hereditaire elle-meme qui est viceuse; pour les maladies infectieuses, levice 

 n'est pas dans la substance elle-meme, mais a cote d'elle, et les produits 

 sexuels servent seulement de vehicule a un parasite capable d'engendrer 

 plus tard une maladie generate. " Y. Delage, La Structure du Protoplasma 

 et les Theories sur F Heredite. Paris, 1895. 



