Volume 1

Modern medicine : its theory and practice / in original contributions by American and foreign authors ; edited by William Osler ; assisted by Thomas McCrae.

  • William Osler
Date:
1907-1910
Catalogue details

Licence: Public Domain Mark

Credit: Modern medicine : its theory and practice / in original contributions by American and foreign authors ; edited by William Osler ; assisted by Thomas McCrae. Source: Wellcome Collection.

    54/986 (page 30)
    to the R features; and so with parents possessing the R character. The hybrids D [R], however, in each subsequent generation produce the defi¬ nite proportion of dominants, hybrids, and recessives. When the species differ in several pairs of features, the result, though following the same lines as regards each individual pair, becomes much more complicated, although eventually, after several generations, individ¬ uals of the pure parent types are reproduced In other words, by this ex¬ clusive inheritance the results of a mesalliance in the pedigree may be completely cast out and the stock become once more pure. Castle and Allen have demonstrated the existence of the same law in animals— mice—in regard to coat color. 4. Production of New Features and a New Strain by Cross-Breed¬ ing.—There is shown, it may be added, an equal likelihood that the mating of two individuals which, as regards two pairs of contrasted characters (or allelomorphs), exhibit each reversely a dominant feature as regards the one and a recessive as regards the other will result in the development of definite proportions of individuals resembling nether stock but showing a commingling of two dominant or two recessive fea¬ tures. If either of these new forms be mated strictly with other individ¬ uals of the same type there results a new strain or variety breeding true and distinct from either ancestral stock. Thus, to quote Bateson, if a red variety of some plant, say a stock, be crossed with a cream-colored variety, while the hybrids of the first generation are red (red being domi¬ nant), in the second generation a small proportion (three-sixteenths of the total progeny) of plants may appear with flowers neither yellow nor red but white, and these white-flowered forms, if crossed among them¬ selves or allowed to undergo self-fertilization, yield a permanent white strain. The explanation here is that the one ancestral form has red sap (D) with colorless corpuscles (R) floating in it, the other, colorless sap (R) with cream-colored corpuscles (D). In this way some of the second generation come to possess a mingling of the characters, color¬ less corpuscles and colorless sap. This, it may be noted, is the basal principle underlying the production of new strains or varieties by the horticulturist and undoubtedly helps to explain the production of one order of the “sports” to which we refer in a later paragraph. Interesting as it is, we shall not here enter into a detailed account of the Mendelian doctrine, which has provided keen activity of late, more particularly among English and American biologists; to discuss it adequately would demand many pages. A consideration of its bearings upon the inherit¬ ance of morbid conditions is given by Bateson, the leader of the school, in a lecture to the Neurological Society of London.1 In the human race, where not only there is no self-fertilizing but con¬ jugation between those of the same stock is largely prohibited, and where, again, the number of points of difference between the individuals is extraordinarily great, Mendel’s law can rarely be brought to apply, save in the most general terms. In any case it does not explain, any more than does the Ir.w of gravitation. It helps us, however, to harmonize data otherwise not a little confusing—to recognize dominant features in the members of a family (such as, for example, the well-known Hapsburg 1 British Medical Journal, 1906, ii, 61