HISTORICAL. 199 



pulmonary arteries, becomes the aorta and supplies all the organs of the body. 

 The veins of the greater circulation empty into the right, those of the lesser circu- 

 lation into the left, auricle. Fishes and amphibia possess a dilated bulbus arterio- 

 sus at the beginning of the aorta; and this is partly covered with strong muscular 

 tissue. Among reptiles the saurians (///) possess' two separate auricles, but the 

 two ventricles are only imperfectly divided. The aorta and pulmonary artery 

 arise separately from the latter. The venous blood of the greater and the lesser 

 circulation, which flows separately into the right and the left auricle, becomes 

 mixed in the cavity of the ventricle. In some reptiles, however, the opening in 

 the ventricular septum appears to be capable of (voluntary or reflex?) closure. 

 The complete separation of the two halves of the heart in turtles is shown in 

 Fig. IV. The lower vertebrates possess valves at the orifice of the vena cava, 

 which are rudimentary in birds and in some of the mammals. All birds and 

 mammals, like man, possess two separate auricles and two separate ventricles. In 

 the halicore, a graminivorous marine animal resembling the whale, the ventricular 

 portion of the heart is divided by a deep cleft into two halves. In bats the veins 

 of the wings pulsate. The lowest of all vertebrates, the amphioxus, has no heart 

 at all, but rhythmically contracting vessels. 



Of the ductless glands, the thymus and the spleen are found constantly in 

 vertebrates. The latter is wanting only in the amphioxus and in a few fishes. 



Among invertebrates closed blood-channels with pulsating movements are 

 only found occasionally, as, for example, in the echinoderms (sea-urchin, star-fish, 

 holothurians) and in the higher worms. Insects possess in the dorsal region a 

 central circulatory organ (the "dorsal vessel"), a contractile, longitudinal duct, 

 capable, by virtue of its muscle-fibers, of dilating, and provided with valves 

 which propels the blood rhythmically into the interstices of all the organs. Insects 

 have no closed circulation. Shell-fish and snails have a heart and lacunar blood- 

 channels. Cephalopods (sepia, cuttle-fish) have three hearts: an arterial, simple 

 body-heart, and two venous, simple branchial hearts, one at the base of each gill. 

 The circulation in most of these animals is closed. The lowest animals have 

 either (multiple) pulsating vacuoles, which propel the colorless (blood-) juice into 

 the soft body-parenchyma, like the infusoria; or they are totally devoid of any 

 kind of vascular apparatus, the circulation of the juices being effected by the 

 movements of the body (gregarines) . In the group of celenterates (polyps, jelly- 

 fish) there is a "water-vascular system," which conveys the nutritive juice directly 

 from the digestive cavity, and, at the same time, acts as a respiratory organ, as 

 the water (which contains oxygen) passes through the system of tubes. 



HISTORICAL. 



The ancients (Empedocles, born 473 B. C.) were familiar with the movement 

 of the blood, but were ignorant of the "circulation." According to Aristotle 

 (384 B. C.) the heart, the acropolis of the body (which is present in every blood- 

 animal), prepares the blood within its cavities and sends it through the arteries 

 as a nutrient fluid to all the different parts of the body, like a system of constantly 

 dividing brooks, irrigating the land and moistening and fertilizing it. The blood 

 however, never flows back to the heart. 



Praxagoras (341 B. C.) named the "arteries" (as well as the trachea); he was 

 the first to distinguish arteries from veins. Together with Herophi-lus and Erasis- 

 tratus (300 B. C.) , trje famous physicians of the Alexandrian school, he is responsible 

 for the erroneous view, based on the fact that arteries are empty after death, 

 that the arteries contain air conveyed to them through the respiration (hence the 

 name "artery"). Galen (131-203 A. D.) refuted this error by vivisection. "When- 

 ever,", he says, "I injured an artery I saw blood escape. And when I tied a 

 portion of an artery by means of two" ligatures at either extremity, I showed that 

 the included portion was full of blood." 



Even then the theory of the exclusively centrifugal movement of the blood 

 was maintained; it was erroneously supposed that communicating orifices existed 

 in the septum between the right and the left heart. 



Miguel Serveto (a Spanish monk, who was burned as a heretic in Irene va i: 

 1553 at Calvin's instigation) was the first to show that the septum of the heart 

 has no openings. He, therefore, searched for a communication between the right 

 and the left heart and thus succeeded, in 1546. in discovering the lesser circulation: 

 "fit autem communicatio haec non per parietem cordis medium (septum), ut vulgo 



