1246 LIFE : OUTLINES OF GENERAL BIOLOGY 



point clear, taking the case of crossing an ordinary normal mouse 

 with the peculiar variety, already mentioned, called the Japanese 

 or waltzing mouse, which goes round and round without any par- 

 ticular reason. This waltzing mouse has some queer kink in its 

 nervous sj^stem. What the peculiarity is we do not clearly know; 

 probably some penetrating defect in the inheritance of the mouse 

 as regards its nervous system— a defect that finds diverse expressions. 

 For instance, the waltzing mouse is deaf for the whole of its life 

 except for a day or two. It is full of peculiarities, which seem to hang 

 together. Now if the waltzing mouse be paired with the normal 

 mouse, the offspring will be all apparently normal — the peculiarity 

 does not find expression; it is latent, not patent! All the offspring 

 of the first generation are apparently normal mice, but when these 

 are paired with one another, or with others of similar history, 

 25 per cent, of their progeny are pure normal, 25 per cent, are pure 

 waltzers, and 50 percent, are, like their immediate parents, appar- 

 ently normal, but with waltzingness in their germinal constitution. 

 Now let us think of the waltzingness as comparable to the character- 

 istic of a defective human being. As long as one of these apparently 

 normal individuals, with waltzingness or deficiency in the constitu- 

 tion, pairs with a thoroughly normal individual, everj^thing in the 

 progeny will look well; the normality will be dominant over the 

 recessive waltzingness, and all the offspring will be apparently 

 normal. But suppose these apparently normal defectives, whose 

 deficiency is masked, pair amongst themselves, then in the next 

 generation one-quarter of the children will be patent defectives. 

 As long as the masked human defectives marry normals the children 

 will be apparently normal, for normality is dominant over deficiency 

 in the great majority of cases; but if the masked defectives marry 

 among themselves, then on an average one in four children will be 

 patently defective. This Mendelian interpretation of the masking 

 and the subsequent disclosure of deficiency is of great social im- 

 portance. 



Let us think for a little of another problem — the transmissibility 

 of acquired characters. According to Weismann's definition, an 

 acquired character is a peculiarity of the body directly resulting from 

 some peculiarity of nurture — whether it be environmental, nutri- 

 tional or functional. There is no doubt that modifications may be 

 induced in the individual as the direct results of some peculiarity in 

 the individual nurture. The question is whether these modifications 

 — for good or ill — can be handed on to the next generation in any 

 degree; and it is an extraordinarity important question not yet 

 definitel}' answered. 



One remembers Spencer's remarkable declaration — very rash for 

 such a big-brained man. He said: "Either there has been inheritance 

 of acquired characteristics or there has been no evolution." But many 



