GENETICS — MORGAN 357 



whether the organizer acts first on the protoplasm of the neighboring 

 region with which it comes in contact, and through the protoplasm 

 of the cells on the genes ; or whether the influence is more directly on 

 the genes. In either case the problem under discussion remains ex- 

 actly where it was before. The conception of an organizer has not 

 as yet helped to solve the more fundamental relation between genes 

 and differentiation, although it certainly marks an important step 

 forward in our understanding of embryonic development. 



GENETICS AND MEDICINE 



That man inherits his characters in the same way as do other ani- 

 mals there can be no doubt. The medical literature contains hun- 

 dreds of family pedigrees, in which certain characters, usually 

 malformations, appear more frequently than in the general popula- 

 tion. Most of these are structural defects; a few are physiological 

 traits (such as haemophilia) ; others are psychopathic. Enough is 

 already known to show that they follow genetic principles. 



Man is a poor breeder — hence many of these family pedigrees are 

 too meager to furnish good material for genetic analysis. When an 

 attempt is made to combine pedigrees from different sources in order 

 to insure sufficient data, the question of correct diagnosis sometimes 

 presents serious difficulties, especially in the older materials; but 

 with the very great advances that have been made in medical diag- 

 nosis in recent years this difficulty will certainly be less serious in 

 the future. 



The most important contribution to medicine that genetics has 

 made is, in my opinion, intellectual. I do not mean to imply that 

 the practical applications are unimportant, and I shall in a moment 

 point out some of the more obvious connections, but the whole subject 

 of human heredity in the past (and even at the present time in 

 uninformed quarters) has been so vague and tainted by myths and 

 superstitions that a scientific understanding of the subject is an 

 achievement of the first order. Owing to genetic knowledge medi- 

 cine is today emancipated from the superstition of the inheritance 

 of maternal impressions : it is free from the myth of the transmission 

 of acquired characters, and in time the medical man will absorb 

 the genetic meaning of the role of external environment in the 

 coming to expression of genetic characters. 



The importance of this relation will be seen when it is recalled 

 that the germ-plasm, or, we say, the genie composition of man is a 

 very complex mixture — ^much more so than that of most other ani- 

 mals, because in very recent times there has been a great amalgama- 

 tion of many different races owing to the extensive migration of the 

 human animal, and also because man's social institutions help to 



