66 ADAPTATION AND DISEASE 



acting from without v/pon the germ cells haw led to the acquire- 

 ment of conditions of defect. To us as medical men it is a minor 

 point whether there is inheritance of the exact defect seen 

 in the parent who has been subjected to a given form of 

 intoxication ; the essential fact is that soluble poisons acting 

 upon the tissues in general of the parent can act also upon and 

 modify the germ cells, so that at some definite period such change 

 occurs in the constitution of those germ cells that the constitu- 

 tion of the offspring is permanently affected, and that its germ 

 cells in their turn are incomplete in molecular structure. 



It is not a little interesting that alcohol, lead, and bacterial 

 toxines in general have a profound, we might almost say specific 

 effect upon the nervous system in the adult or adolescent in- 

 dividual, and that they are so peculiarly liable to influence the 

 nervous system of the offspring. To this aspect of the matter 

 I shall refer later. 



Such " parallel induction " of defects in both the body cells 

 and germ cells has been repeatedly noted of recent years by 

 workers in experimental genetics, the case that has afforded the 

 greatest amount of discussion being that of Salamandra maculosa, 

 as studied over a long series of years by Kammerer and recorded 

 in the Archiv fur Entwickelungsmechanik. This is a salamander 

 which normally hatches its eggs in the water, in which they 

 develop into tadpoles with gills. Very gradually Kammerer 

 accustomed the parent forms to live entirely on land in a damp 

 atmosphere, and with this, in place of producing some sixty to 

 seventy eggs the females became viviparous, giving birth to at 

 most six or seven young, with the tadpole or gill-bearing stage 

 completely suppressed, and breathing by lungs. That here the 

 environment to which the parents have been subjected tells 

 not merely on the growing embryos, but upon the germ cells, 

 is evidenced by the fact that when the members of this second 

 generation are supplied freely with water they produce tad- 

 poles, it is true, but now the metamorphosis from the water- 

 living and gill-breathing to the land-living and lung-breathing 

 stage, instead of taking months, as in the case of the normal 

 spotted salamander, occurs in the course of a few days. 



Walter, 1 1 observe, objects that this is not a case of inherit- 



1 Genetics, an Introduction to the Study of Heredity, New York, The Mac- 

 millan Company, 1913, p. 90. 



