The physiology of the circulation in plants, in the lower animals, and in man : being a course of lectures delivered at the Surgeons' Hall to the president, fellows, etc. of the Royal College of Surgeons of Edinburgh, in the summer of 1872 / by J. Bell Pettigrew.

  • Pettigrew, James Bell, 1834-1908.
Date:
1874
Catalogue details

Licence: Public Domain Mark

Credit: The physiology of the circulation in plants, in the lower animals, and in man : being a course of lectures delivered at the Surgeons' Hall to the president, fellows, etc. of the Royal College of Surgeons of Edinburgh, in the summer of 1872 / by J. Bell Pettigrew. Source: Wellcome Collection.

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    so on until we arrive at a degree of differentiation and com- pleteness which, while it commands the reverence, must elicit the admiration of every one who reflects. In the human circulation nearly all the links are present, and it is only by a knowledge of these, as they exist in the lower grades of life, that we can hope to put them in their proper places, when we come to generalise. In the plant and medusa there is no trace either of a heart or pulsatile vessel. In the insect the heart is absent, but a pulsatile vessel makes its appearance. In the fish a heart, consisting of two cavities, is found. In the serpent those cavities are increased to three ; and in birds and mammals to four. The number of the cavities depends to a certain extent on the nature of the respiration, and this in its turn modifies the temperature of the blood. In the fish breathing is effected, and the blood aerated, by the gills; one cavity (the auricle) receiving the blood from the system ; the other (the ventricle) forcing it directly into the gills, and, through them, indirectly into the' system. In the serpent breathing is effected, and the blood aerated, by the aid of lungs ; two cavities (the auricles) receiving the blood from the lungs and from the . system ; one cavity (the ventricle) forcing it through the lungs and through the system. In the reptile the circulation is of a. mixed character, the arterial and venous blood blending in the ventricle of the heart. In the bird and mammal the heart consists of four cavities—two auricles and two ventri- cles ; the auricles receiving the blood from the system and from the lungs ; the ventricles propelling the blood through the lungs and through the system. This object is attained by a cross circulation—the right auricle receiving venous or dark blood, the left auricle arterial or bright red blood ; the right ventricle propelling venous or dark blood, the left one arterial or bright blood. The differentiation observable in the cavities of the heart is preceded by a similar differentiation in the channels and vessels through which the nutritious juices flow ; the elaboration of the heart and vessels necessitating the presence of valves, which vary in number according to the complexity of the circulatory apparatus. ' In the lowest or- ganised plants, such as the fungi, algae, etc., and in the lower classes of animals, as the polypi, actiniae, and a great part of