PECULIARITIES OF CIRCULATION IN DIFFERENT PARTS. 357 



bo poured into some neighboring serous cavity, producing dropsy. Thus it 

 happens that such effusions may often be traced to that state of deficient 

 vigor of the system, which peculiarly manifests itself in want of tone of the 

 bloodvessels; and that it is relieved by remedies which restore this. In 

 many young females of leucophlegmatic temperament, for example, there. 

 is a tendency to swelling of the feet, by oedematous effusion into the areolar 

 tissue, in consequeiiee of the depending position of the limbs; the oedema 

 disappears during the night, but returns during the day, and is at its maxi- 

 mum in the evening. And the congestion which frequently manifests itself 

 in the posterior parts of the body, towards the close of exhausting diseases 

 in which the patient has lain much upon his back, is attributable to a simi- 

 lar cause ; of such congestion, effusions into the various serous cavities are 

 frequent results; and such effusions, taking place during the last hours of 

 life, are often erroneously regarded as the source of death. To the same 

 cause we are to attribute the varicose state of the veins of the leg, which is 

 so common amongst persons of relaxed fibre, and especially in those whose 

 habits require them to be much in the erect posture ; and this distension oc- 

 casionally proceeds to complete rupture, the causes of which are fully eluci- 

 dated by the experiments just cited. 



6. Peculiarities of the Circulation in different Parts. 



277. In several portions of the Human body, there are certain varieties 

 in the distribution and in the functional actions of the bloodvessels, which 

 should not be omitted in a general account of the Circulation. Of. these, 

 we have in the first place to notice the apparatus for the Pulmonary circula- 

 tion ; the chief peculiarity of which is, that venous blood is sent from the 

 heart, through a tube which is arterial in its structure, whilst arterial blood 

 is returned to the heart, through a vessel whose entire character is; that of a 

 vein. The movement of the blood through these is considerably affected by 

 the physical state of the lungs themselves ; being retarded by any causes 

 which can occasion pressure on the vessels (such as over-distension of the 

 cells with air, 1 obstruction of their cavity by solid or fluid depositions, or by 

 foreign substances injected into them, etc.); and proceeding with the great- 

 est energy and regularity when the respiratory movements are freely per- 

 formed. The Portal circulation, again, is peculiar, in being a kind of offset 

 from the general or systemic circulation, and also in being destitute of 

 valves; and it may be surmised with much probability, that the purpose of 

 their absence is, to allow of an unusually free passage of blood from one 

 part of that system to another, during the very varying conditions to which 

 it is subjected. Another very important modification of the Circulating 

 system, is that which presents itself within the Cranium. From the circum- 

 stance of the cranium being a closed cavity, which must be always filled 

 with the same total amount of contents, the flow of blood through its vessels 

 is attended with some peculiarities. The pressure of the atmosphere is here 

 exerted, rather to keep the blood in the head, than to force it out ; and it 

 might accordingly be inferred, that, whilst the quantity of cerebral matter 

 remains the same, the amount of blood in the cranial vessels must also be 

 invariable. This inference appeared to derive support from the experiments 

 of Dr. Kellie. 2 On bleeding animals to death, he found that, whilst the re- 

 mainder of the body was completely exsanguine, the usual quantity of blood 

 remained in the arteries and veins of the cranium; but that if an opening 



1 See Quincke and Pfeiffcr, Ueber den Blut^troni in die Lungen, Reichert und Du 

 Bois-Reymond's Archiv, 1871, p. 90. 



2 Edinburgh Medico-Cliirurgiual Transactions, vol. i. 



