Text-book of human physiology : including histology and microscopical anatomy with especial reference to the practice of medicine / by L. Landois.

  • Leonard Landois
Date:
[1904], ©1904
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Licence: Public Domain Mark

Credit: Text-book of human physiology : including histology and microscopical anatomy with especial reference to the practice of medicine / by L. Landois. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    of the nervi erigentes). The vasomotor nerves may be excited reflexly; also through irritation of the sciatie. The internal os is especially rich in nerves. After birth the entire uterus is deprived of its mucosa (decidua); its inner surface, therefore, is like a wound-surface, upon which a new membrane is formed, with a secretion at first resembling an infusion of meat, later containing a larger number of cells, and finally becoming mitcoid (lochia). The thick muscular layer of the uterus undergoes gradual reduction through partial fatty degeneration of its fibers. Within the hunen of the large vessels an obliterating connective- tissue hyperplasia begins from the intima, and in the course of several months diminishes the lumen of the vessels or occludes them. The unstriated muscle- fibers of the media undergo fatty degeneration. The relatively large blood- spaces at the placental site are plugged by thrombi, and the latter are invaded by connective-tissue from the walls of the vessel. After birth secretion of milk sets in, with a peculiar effect upon the vas- cular nervous system (milk-fever?), an increased amotmt of blood being sent to the mammary glands on the second or third day. The institution of the first respiratory movements in the new-born is discussed on p. 755. COMPARATIVE. HISTORICAL. Embryology must not omit to take into consideration the general develop- ment of the entire animal kingdom. The question How have the inniunerable animal forms at present living originated? has in part been answered by the statement that all species have been created as such from the beginning, every form is an embodied idea of creation; all species, further, remain as such without alteration; the constancy of species prevails. In opposition to this view, held by Linnaeus, Cuvier, Agassiz, and others, Jean Lamarck in 1809 developed the doctrine of the unity of the animal kingdom, embodying the old idea of Empedocles, namely that all species have developed by variation from a few funda- mental species, that originally only a few fundamental species of lower formation existed, from which the new, numerous species have evolved—a view svipported also by Geoffroy St. Hilaire and Goethe. After a long interval this thought was de- veloped in a particularly fruitful way by Charles Darwin (1859). ^^ supported his monistic conception of the animal kingdom by a description of the manner in which gradual evolution of species can be explained. Among the creatures of the earth there takes place, for the preservation of life, a struggle of all against all, and from this struggle for existence only those will go forth victorious that are char- acterized by particularly striking qualities. Such qualities: strength, speed, size, color, fruit'fulness, are, however, hereditary, and thus it is evident that, in this manner, to a certain degree through natural selection, an uninterrupted process of improvement and thereby a gradual variation in species takes place. In addition, the creatures are capable, within certain limits, of adapting themselves to their surroundings and the prevailing necessities of external influences. In this way, certain organs may tmdergo a useful transformation, while inactive parts can gradually undergo involution to rudimentary organs. The gradual alteration of animal forms thus resulting through natural selection finds its jirototype in artificial selection among animals and plants. It is known, for instance, that breeders of animals are able, in a relativel}^ short time, to produce variations in form that are much more considerable than those between two well- characterized species of animals. Thus, the skull of a mastift and that of an Italian grayhound exhibit a much greater difference than that of a fox as com- ])ared with that of a similar species of dog. As in the case of artificial selection, however, there is observed a sudden reversion to an ancestral type, so also in the development of natural species atavism may occur. Obviously the ease of varia- tion is increased by the widespread distribution of a given species in different climates, as in this way different influences become operative. Thus, the migra- tion of organisms may gradually contribute to variations in species (M. Wagner's law of migration). Inheritance of mutilations does not occur. Without entering upon the details in the development of the different varieties of animals, the biogenetic fundamental law may be briefly discussed. According to this, the history of the individual (ontogeny) is a brief repetition of the history of the family (phylogeny). Applied especially to man, this law implies that the separate stages in the development of the human embryo, for example its exist- ence as a unicellular ovum, as a collection of cells after cleavage has been completed, as a cellular vesicle (germinal vesicle), as a two-layered vesicle, as a being without