A compendium of the veterinary art : containing plain and concise observations on the construction and management of the stable ... the structure and economy of the horse ... a copious materia medica and pharmacopœia / by James White.

  • White, James, -1825
Date:
1842
Catalogue details

Licence: Public Domain Mark

Credit: A compendium of the veterinary art : containing plain and concise observations on the construction and management of the stable ... the structure and economy of the horse ... a copious materia medica and pharmacopœia / by James White. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    derive nourishment and purification by a sort of imbibition from the mother's blood. The ovum, on leaving the ovaries, is furnished with a mem- brane, called the Amnios, which afterwards increases in size, and furnishes a liquid in which the foetus floats, comparatively free from danger, and in all the ease and luxury of an hydraulic bed. It is supported in its situation by the umbilical cord, or navel string, which is nearly three feet in length, and is composed of the blood vessels, and a canal communicating with the bladder, and proceeding from the navel of the foetus, and passing to the deciduous membranes of the mare. This canal is called the urachus, and serves to convey away the superfluous water that the foetal bladder would be incapable of containing. The circulation of the blood in the foetus, it is evident, must be very different fi'om that after birth. Nourishment is not afforded by the stomach, bile is not secreted by the liver, nor is the blood purified hy the lungs: these organs are only supplied with nourishment suflBcient for their own support and increase. The arteries belonging to the maternal portion of the placenta terminate partly in veins, and partly in exhalent surfaces : from these exhalent surfaces, the minute branches of the umbilical veins of the foetus absorb blood in a comparatively red and purified state: they convey this blood into the foetal circulation through the vein, which, in the animal after birth, is wholly en- gaged in supplying the liver. It will thus be seen that the umbilical veins convey red blood, and the umbilical arteries black blood, contrary to the usual custom. The blood from the um- bilical veins, as well as the lower part of the body, enters both - sides of the heart at once, and a small portion is thence sent into the lungs from the right ventricle, whilst the largest portion is distributed to the system from the left ventricle. There is a communication, too, between the aorta and the pulmonary artery, by which the blood not required by the lungs is sent into the system through the aorta. It will thus be seen that the heart of the foetus, though double in its construction, is single in its office; and, in this respect, is very analogous to the single heart of some cold-blooded animals. No sooner, however, does the animal breathe, than the right side of the heart has an inde- pendent office to perform, and the communications before spoken of are closed up. — Ed.] G 4
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