THE HEREDITARY TRANSMISSION OF 

 MICRO-ORGANISMS. 



IT is well known that in the construction of many of the 

 theories of heredity the doctrine of the transmission of 

 acquired characters has obtained considerable prominence. 

 The hypothesis of Lamarck rendered it necessary to assume 

 that structural characters which had arisen from the use or 

 disuse of organs, became an integral part of the individual 

 and reappeared in the descendants, and although the appli- 

 cation of this idea became greatly restricted when the 

 principle of natural selection was established, it is only 

 within the last few years that the transmission of acquired 

 characters has been considered as unproven, and the in- 

 stances put forward in support of this view to be capable 

 of a different explanation. It may be admitted that mutila- 

 tions and permanent injuries can be included among acquired 

 characters, and the structural and functional modifications of 

 the individual which occur in disease may persist, and 

 therefore also be considered as definite morphological or 

 physiological changes. Mutilations apparently do not pass 

 from parent to offspring, and this has been especially pointed 

 out by Weismann and his followers, since, if heredity is 

 capable of explanation on the hypothesis of the continuity 

 of germ-plasm contained in definite reproductive cells, any 

 change in the structure or modes of activity of the essential 

 body or somatic cells would not be transmitted. An iden- 

 tical line of argument also negatives the belief that diseases 

 can be inherited, and this view was maintained by Weismann 

 in his well-known criticism on the transmission of experi- 

 mental epilepsy ; the symptoms in this hereditary disease he 

 considered might be due to some unknown microbe which 

 found its nutritive medium in the nervous tissues and 

 was transmitted in the reproductive cells. The question 

 whether micro-organisms can actually pass from parent to off- 

 spring is one which has been carefully investigated, whereas 



