552 ANNUAL. REPORT SMITHSONIAN INSTITUTION, 1918. 



it be granted that germ plasm existing to-day is the lineal descendant 

 of plasm which has existed since the origin of life, this statement re- 

 quires some qualification. The unexpended germ cells not only die, 

 of course, at the death of the individual, like any other piece of pro- 

 toplasm, but they may die, or at all events lose their capacity for 

 reproduction (which comes to the same thing), while the ordinary 

 somatic cells are still alive. This commonly takes place in women 

 between the fortieth and fiftieth year. Now, it has been noticed by 

 several observers that children born toward the end of the female 

 reproductive period tend to be feebler than those born while the 

 generative organs are in full vigor. Possibly this, in part, may be 

 due to a senility of the maternal tissues which nourish the seed, but 

 it is equally likely to be due to a senility of the seed itself, so that 

 there is some ground for thinking that senescence may be a possible 

 cause of pathological germ variations. 



Again, there are certain infusoria, which, while ordinarily multi- 

 plying by fission, from time to time undergo a form of conjugation 

 not unlike that which occurs between the sperm and germ cells in 

 human beings. It was shown by Maupas that, if this periodical con- 

 jugation is prevented, the offspring resulting from subsequent fissions 

 gradually undergoes a form of degradation until the whole group 

 eventually becomes extinct. Prof. Marcus Hartog argues from this 

 and similar researches made by other inquirers that conjugation or 

 fertilization plays an important part in warding off senescence. Is 

 such introduction of fresh blood necessary to ward off senescence 

 and prevent germinal impairment in the case of higher animals, 

 human beings in particular? With regard to certain domestic ani- 

 mals, there is reason to think that close in-breeding is followed by 

 a gradual deterioration of offspring; and experienced breeders are 

 practically unanimous that the effect of this is to produce debility, 

 abnormalities, and eventually sterility. As Sir Francis Darwin 

 says, " it is generally admitted that degeneration either in constitu- 

 tion or in other ways does ultimately ensue; so that at any cost the 

 breeder is absolutely compelled to admit blood from another family 

 or strain of the same race." In the case of human beings, however, 

 in-and-in breeding to this extent is practically unknown; and it is 

 therefore unlikely that senescence of the germ plasm from such a 

 cause plays any practical part in the production of degeneracy. At 

 the same time it is to be remarked that the effect of consanguineous 

 marriages is to intensify any existing defect; and the same is true 

 where mating is rigidly restricted to the members of any one small 

 section of society. We are apt nowadays to bewail the not infrequent 

 union of members of our old and formerly exclusive aristocracy with 

 chorus girls and the like. The process may be attended with a serious 

 decline in " form" and manners; but it is possible that it may possess 



