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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



imagines them to be invisible, by reason of their 

 small size and their closure by the refrigeration 

 of the heart, after death. Nevertheless, he can- 

 not doubt their existence, partly because the sep- 

 tum presents a great number of pits which ob- 

 viously lead into its substance as they narrow, 

 and, as he is so fond of saying, " Nature makes 

 nothing in vain ; " and, partly, because the vena 

 cava is so large, in comparison with the vena 

 arteriosa, that he does not see how all the blood 

 poured into the ventricle could be got rid of, if 

 the latter were its only channel. 



Thus, for Galen, the course of the blood 

 through the heart was — on the right side, in by 

 the vena cava, out by the vena arteriosa and the 

 pores of the septum ; on the left side, in by the 

 pores of the septum and by the arteria venosa, 

 out by the aorta. What, now, becomes of the 

 blood which, filling the vena arteriosa, reaches 

 the lungs ? Galen's views are perfectly definite 

 about this point. The vena arteriosa communi- 

 cates with the arteria venosa in the lungs by nu- 

 merous connecting channels. During expiration, 

 the blood which is in the lungs, being compressed, 

 tends to flow back into the heart by way of the 

 vena arteriosa ; but it is prevented from doing 

 so, in consequence of the closure of the semi- 

 lunar valves. Hence, a portion of it is forced 

 the other way, through the anastomoses into the 

 arteria venosa ; and then, mixed with " pneuma," 

 it is carried to the left ventricle, whence it is 

 propelled, through the aorta and its branches, all 

 over the body. 



Galen not only took great pains to obtain ex- 

 perimental proof that, during life, all the arteries 

 contain blood and not air, as Erasistratus sup- 

 posed ; but he distinctly affirms that the blood 

 in the left ventricle and in the arteria venosa is 

 different from that in the right ventricle and in the 

 veins, including the vena arteriosa ; and that the 

 difference between the two lies in color, heat, and 

 the greater quantity of " pneuma " contained in 

 arterial blood. Now, this "pneuma" is some- 

 thing acquired by the blood in the lungs. The 

 air which is inspired into these organs is a kind 

 of aliment. It is not taken bodily into the veno- 

 sa arteria and thence carried to the left ventricle 

 to fill the arterial system, as Erasistratus thought. 

 On the contrary, Galen repeatedly argues that 

 this cannot be the case, and often refers to his 

 experimental proofs that the whole arterial sys- 

 tem is full of blood during life. But the air sup- 

 plies a material kindred to the " pneuma," out of 

 which and the blood the " pneuma " is concocted. 

 Hence, the contents of the arteria venosa arc large- 



ly composed of " pneuma," and it is out of the mixt- 

 ure of this with the blood which filters through 

 the septum that the bright " pneumatic " blood 

 found in the arteries, and by them distributed over 

 the body, is formed. The arteria venosa is a chan- 

 nel by which " pneuma " reaches the heart, but 

 this is not its exclusive function ; for it has, at 

 the same time, to allow of the passage of certain 

 fuliginous and impure matters which the blood 

 contains, in the opposite direction ; and it is for 

 this reason that there are only two valves where 

 the arteria venosa enters the ventricle. These, 

 not fitting quite tightly, allow of the exit of the 

 fuliginous matters in question. 



Modern commentators are fond of pouring 

 scorn upon Galen, because he holds that the 

 heart is not a muscle. But, if what he says on 

 this subject is studied with care and impartiality, 

 and with due recollection of the fact that Galen 

 was not obliged to use the terminology of the 

 nineteenth century, it will be seen that he by no 

 means deserves blame, but rather praise, for his 

 critical discrimination of things which are really 

 unlike. 



All that Galen affirms is, that the heart is 

 totally unlike one of the ordinary muscles of the 

 body, not only in structure, but in being inde- 

 pendent of the control of the will ; and, so far 

 from doubting that the walls of the heart are 

 made up of active fibres, he expressly describes 

 these fibres and what he supposes to be their 

 arrangement and their mode of action. The 

 fibres are of three kinds, longitudinal, transverse, 

 and oblique. The action of the longitudinal 

 fibres is to draw in, that of the circular fibres to 

 expel, and that of the oblique fibres to retain, 

 the contents of the heart. How Galen supposed 

 the oblique fibres could execute the function as- 

 cribed to them, I do not know ; but it is clear 

 that he thought that the activity of the circular 

 fibres increased, and that of the longitudinal 

 fibres diminished, the size of the cavities which 

 they surrounded. Nowadays we term an active 

 fibre muscular; Galen did not, unless, in addi- 

 tion, it possessed the characters of voluntary 

 muscle. 



According to Galen, the arteries have a sys- 

 tole and diastole (that is, a state of contraction 

 and a state of dilatation), which alternate with 

 those of the ventricles, and depend upon active 

 contractions and dilatations of their walls. This 

 active faculty of the arteries is inherent in them, 

 because they are, as it were, productions of the 

 substance of the ventricles which possess these 

 faculties ; and it is destroyed when the vital con- 



