In heart disease the chief work of the latter half of the 19th century was, in the first quarter, such clinical work as that of William Stokes and Peter Mere Latham (1789-1875); and in the second quarter the fuller comprehension of the vascular system, central and peripheral, with its cycles and variations of blood pressure, venous and arterial.
The ramifications of the arteries convey the blood to all parts of the body, and it finally reaches the venous sinuses, the chief of which are the pedal, the pallial and the median-ventral.
Dropsy of the serous cavities is very commonly merely part of a general anasarca, although occasionally it may be, as in the case of ascites, the sequel to an obstruction in the venous return.
This dilatation may be increased by local warmth, and poultices or fomentations are commonly applied to inflamed parts; recently suction apparatus has been used for the same purpose or ligature so as to cause venous stasis (Bier's treatment).
The right and left halves are completely divided by septa, no mixture of the venous and arterial blood being possible, an advance upon reptilian conditions, even the highest.
In Scorpio the completion of the horizontal plate by oblique flaps, so as to form an actual diaphragm shutting off the cavity of the prosoma from the rest of the body, possibly gives to the organs contained in the anterior chamber a physiological advantage in respect of the supply of arterial blood and its separation from the venous blood of the mesosoma.
It receives the three great venous trunks of the body, namely the vena cava superior dextra, the vena cava superior sinistra more dorsally, and the vena cava inferior more to the right and below; the opening of the last is guarded by two prominent valves in place of the mammalian valvula Eustachii.
Much light has been thrown upon the variations of arterial and venous blood pressures by Karl Ludwig (1816-1895) and his many followers: by them not only the diseases of the circulatory system itself are elucidated, but also those of other systems - the nervous, for instance - which depend intimately on the mechanical integrity of the circulation of the blood as well as on the chemical integrity of the blood itself.
The respiratory rhythm is less frequent and the breathing less deep; the heart-beat is less frequent; the secretions are less copious; the pupil is narrow; in the brain there exists arterial anaemia with venous congestion, so that the blood-flow there is less than in the waking state.
The chief varieties of haemorrhage are arterial, venous and capillary.