410 PHYSIOLOGY. 



alone be oxidised ; and, indeed, the fluid would not pass equally into 

 the distant members, but that portion which once found itself in the 

 cavity of such a member would there remain without being equally 

 supplanted by fresh juices. But by this progressive motion of the 

 whole body of juices this partial stagnation is prevented, and each 

 organ furnished equally with fresh juice fitted for assimilation. Both 

 the large streams of blood which run along and between the large 

 lateral stems of the tracheae, are constantly receiving fresh oxygen 

 from the tracheae, and carry with them the fresh lymph secreted by 

 the intestine, and then give off the freshly-oxidised blood to the heart, 

 which, by its rhythmical pulsation, conveys it on, and rejecting it by 

 the free orifice of the aorta, drives it to all the parts of the body. The 

 returning main streams, consequently, are comparable to the arteries of 

 the lungs, or rather, as in the Mollusca, to those large veins which, 

 collecting the blood from all parts of the body, return it through the 

 lungs or bronchise to the heart. The passage of the oxidised blood 

 into the heart is occasioned by its expansion and contraction, which 

 takes place synchronally with the respiratory motion of the whole body, 

 and particularly of the abdomen, and these individual motions of the 

 heart are partially produced by its muscular tunic, and partially by the 

 muscles of the wings which bind it to the dorsal plates. The muscular 

 tunic of the heart contracts itself and makes the systole. The muscles 

 of the wings, by their contraction, again expand the heart, and produce 

 the diastole : when the blood streams in through the apertures and by 

 the former, it is driven into the aorta. Hence throughout the whole 

 body a constant oxidisation of the blood is taking place, as, even in 

 the most remote members, tracheae are distributed, and there oxidise 

 the juices they found. But these juices also do not rest, but participate 

 in the general motion. True venous blood is consequently deficient in 

 insects, and if both the lateral streams have been called veins, this name 

 is only so far tenable as there may be detected in it a returning motion 

 of the blood to the heart. 



243. 



But how can a motion of the blood be imagined without vessels ? 

 This question absolutely appears of great importance, particularly as 

 Carus thought it necessary that there should be vessels in certain parts of 

 the body. This opinion, however, will necessarily be limited to the vessels 



