94 VARIABILITY 



the germ-cell but every cell of the community is a unicellular 

 organism. We may take the human being, as the type best known 

 to us, for an example. Consider first his somatic cells. From the 

 moment the fertilized ovum begins to proliferate to the death of 

 the aged man, strong influences want, plenty, disease, health, 

 hardship, alcohol, and so forth play upon the cells ; yet each cell 

 comes true to its type. Thus all sorts of stimulants and irritants 

 may act on the skin-cells and change them greatly ; but, when the 

 cause of change is removed, the hereditary tendencies are found to 

 be unaltered, for the young cells develop into skin-cells of quite 

 the old kind. I have transferred clippings from an old man's skin 

 to the scalded and denuded arm of a young woman, and they have 

 grown with all the vigour of youth. If a lymphatic gland be 

 diseased (e.g. tuberculous) for a score of years, and recovery then 

 occurs, the cells are still typical of their kind. Disease enfeebles 

 cells, but recovery from disease is evidence of the stability of their 

 hereditary tendencies. Were the latter easily altered, there could be 

 no recovery, and every attack of measles or chicken-pox, maladies 

 in which toxins are abundant and in which the enfeeblement of 

 the cells is shown by the disturbance of function, would be fatal. 

 Consider the cells which line the alimentary canal and the extra- 

 ordinary variety of influences to which they are subjected. Life 

 could not exist if the germ-plasm (idio-plasm) were not resistant. 

 Evidently, then, as a condition essential to the survival of the 

 individual and the persistence of the species, somatic cells hold 

 their hereditary tendencies with extraordinary tenacity with a 

 tenacity as great as that displayed by the microbes of disease. 



152. Further and very decisive evidence is afforded by the 

 extreme stability of plants when propagated by slips and suckers. 

 Centuries may elapse, the plant, continuously so propagated, may 



environment. The whole inquiry was, of course, undertaken to illustrate 

 Weismann's position, that while acquired characters are not inherited, the en- 

 vironment can influence inheritance when one cell is both soma and germ. In 

 biology it has become almost axiomatic to assume that the Protozoa can inherit 

 acquired characters owing to this identity, while in the Metazoa the acquired 

 character of the soma is at the very least not usually inherited. Dr Pearl brings 

 out the all-important point that the gamete in Paramoecium is not, like the non- 

 conjugant cell, markedly influenced by the environment" (Professor Karl 

 Pearson, Nature, Oct. 18, 1906, p. 609). Mr H. S. Jennings has also published 

 observations on Paramoecium. He says nothing concerning conjugant indi- 

 viduals, terms all new characters variations, and concludes, " In order that it 

 may be inherited (by more than one of the progeny), a characteristic must be the 

 result of such a modification of the mother cell as will cause it to behave in a 

 certain way at reproduction." Apparently he means that spontaneous variations 

 tend to be transmitted, but not acquirements. 



