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

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.

1021/1048 (page 1005)

$a coelom, etc., indicate an equal nuniljcr of animal varieties, from which the human race, in the course of inconceivable time, has gradually evolved. The separate steps through which the human race has ])assed in the j)rocess of transformation have been brielly repeated in its embryonal development. This exjiosition has, naturally, not escaped criticism. In any event, the comparison of human de- velopment with relation to the individual organs with the corresponding fully developed organs of the vertebrates is important. Thus also mammals possess in the development of their organs, originally, the simple heart, the visceral clefts, the undeveloped rudimentary brain, the cartilaginous chorda dorsalis, various arrangements of the vascular system, etc., that are peculiar to the lowest forms of vertebrates throughout life. In the higher classes, these incomplete rudimentary structures gradually approach perfection. The moq-jhological differences between man and the gorilla or the chimpanzee are slighter than those between the anthropoids mentioned and other apes. The fossil Pithecanthropus erectus was at first regarded as an extinct link between anthropoids and man, but recently more correctly as a powerful long-armed ape (hylobates, gibbon); the PaljEopithecus sivalensis may occupy an analogous position, with its cranial cavity two-thirds the size of the human cranial cavity and occupying an inter- mediate position between the cranial cavity of the anthropoids and the lower races of man. In detail, however, there are still many difficulties in the way of establishing the Darwinian theory and the fundamental biogenetic law. Historical.—Although the discoveries in ernhvyolngy, more than those in any other branch of biological science, belong especially to modem times, it is, never- theless, interesting to consider the views of the ancients upon different points. Pythagoras (550 B. C.) rejected the theory of spontaneous generation: All life results from seed. According to Alkmacon (580 B. C.) both sexes furnish the fecundating material; the sex of the offspring corresponds to the sex supply- ing the most seed. In development the head is formed first. Anaxagoras (500 B. C.) believed that boys came from the right and girls from the left sexual gland. Empedocles (473 B. C.) recognized the nutrition of the embr\o through the um- bilicus; he was the first to designate the chorion and the amnion, and the segmen- tation of an embryo as complete on the thirty-sixth day. He taught that the first animals of creation w^ere the most incomplete. Hippocrates considered the seventieth day the earliest time for movement and the two hundred and tenth day as term. He taught, with Democritus, that the sexual material came together from all parts of the body (Darwin's pangenesis), thus accounting for the resemblance of the offspring. He observed incubating eggs from day to day, and saw in them the allantois emerge from the umbilicus, and the chick escape on the twentieth day. He taught that seven-month children are viable, explained the possibility of superfetation from the horns of the uterus and de- scribed the lithopedion. According to Plato (430 B. C.) the spinal cord is formed first, as the appendix of which, the brain appears anteriorh'. The writings of Aristotle (born 384 B. C.) are rich in observations of which many have already been cited in the text. He tavight that the embryo received its blood-supply through the vessels of the umbilical cord, and that the placenta absorbs blood from the vascular uterus, as a tree absorbs moisture through its roots. He differen- tiated the polycotyledonary and the diffuse placenta; he attributed the former to ani- mals that do not have complete rows of teeth in both jaws. In the incubated bird's egg he recognized the vessels of the yolk-sac, which convey nourishment from the latter to the embryo, and the vessels of the allantois. The statement is correct also that the chick rests with its head on the right leg, and that the yolk- sac finally enters the body. In the birth of mammals when the head alone is bom it does not breathe. The formation of double monsters is ascribed to the junction of two germs or two embryos lying in close proximity. In the process of conception, the female supplies the material, the male the principle that is responsible for form and movement. With regard to reproduction in the lower animals, reference may be made to the generative arm of the cephalopods, the yolk-sac of the cuttle-fish, the yolk-sac placenta of the smooth shark, the con- jugation of snakes and the absence of the amnion and the allantois in fish and amphibia. Diodes (a contemporary of Theophrastus, bom 371 B. C.) appears to have seen the ovum as early as the second week as a cutaneous vesicle, marked by bloody points (villi?); he describes also the cotyledons of the uterus. Erasist- ratus (304 B. C.) taught the development of the embryo by a neoplastic process in the ovum (epigenesis); he considered scar-formation in the uterus as a cause for sterilitv. His contemporary Herophilus found that the pregnant uterus is closed.$