These terms designate a condition in which the total quantity of blood in the body is in excess. The number of red corpuscles is generally set down as normally about 5 million per cubic millimetre in men, and 4.5 million in women. The number of the white corpuscles is much more variable, increasing, for example, after a meal, but it may be set down as 5000 to 10,000 per cubic millimetre. The first question that arises here is, whether the vascular system is capable of accommodating more blood than it contains normally. There is no difficulty in answering this question in the affirmative. If the vessels as a whole could contain no more blood than they normally hold, then there could be no local variations, no blushing, no increase in the quantity of blood during activity of organs. The capillaries present great variations in the amount of blood they contain at different times, and if we take the whole capillaries of the body into account, it will appear that in them there is a great reserve space which may possibly on occasion be used for the accommodation of an excess of blood. This matter has been brought to the test of experiment, blood being transfused into the circulatory apparatus in animals.

Transfusion of blood is the artificial introduction, into the vascular system, of blood from another person or animal. In the experiments of Worm Muller, which are chiefly of importance here, the defibrinated blood of dogs was injected, with precautions, into the vessels of animals of the same kind. It is not remarkable that the vascular system can accommodate a large additional quantity of blood, but it is remarkable that it should do so with little disturbance to the health of the animal. A quantity equal to a half or three fourths of the blood normally present in the animal may be injected without injuring the health of the animal, and the quantity needs to be double the normal, or over it, before the animal's health is seriously impaired. It might be expected that when the vascular system is thus overfilled the blood-pressure would be greatly raised, but registration of the pressure, by a cannula introduced into the carotid and connected with a kymographion, shows that though during the actual operation there is a rise of pressure, yet it soon falls to within normal limits. If a quantity is injected more than equal to the normal bulk of the blood, then the pressure begins to show remarkable elevations and depressions, and the animal usually dies in the course of the same day or the next. Life is immediately endangered when one and a half times the normal bulk is injected.

When blood is transfused then in large quantity it finds accommodation chiefly in the capillaries and veins, the arteries being relaxed in order to admit of its passing into these, and the blood-pressure is not raised. It appears that the capillaries and veins of the abdominal organs form a great reservoir for the accommodation of excessive blood, and that the blood after transfusion lodges here chiefly.

The excess of blood thus supplied to an animal does not, however, remain permanently as a part of its organism. There seem to be arrangements in the body for disposing of it. Worm Miiller endeavoured to determine what time it took to dispose of a large excess of blood. After the transfusion the animals were starved, and the blood and urine examined at intervals. It was concluded that the fluid of the blood is rapidly disposed of, being excreted by the urine. A few hours after transfusion much of the excess of liquor sanguinis had already gone, and even when a quantity equal to 60 to 80 per cent, of the entire blood was injected, the whole excess had disappeared in the course of two or three days. The rapid disposal of the liquor sanguinis leaves the blood-corpuscles greatly in excess, and the rate of disappearance was determined by counting them by means of Malassez' method. If the quantity transfused is small, the corpuscles may be disposed of in a few days; but in the case of large transfusions it may take two or even three weeks. In this comparatively short period of time, however, the whole excess of blood, both plasma and corpuscles, is removed, and we may infer that there are arrangements in the body for the regulation of the amount of blood.

These experiments all refer to the transfusion of defibrinated blood. If blood is injected when just about to coagulate, or if when it has just begun to coagulate some of the serum is pressed out and injected, then in some cases the animal dies rapidly with symptoms referable to pulmonary embolism. The blood in the right side of the heart and pulmonary artery is found after death to be coagulated. The explanation of this is that, at the time of coagulation of the blood, the substances resident in the leucocytes necessary to coagulation are set free. It appears that even a small quantity of these substances introduced in the free state into the blood of a living animal induces coagulation of it. The importance of these facts in regard to transfusion in human beings will not be overlooked.

Hitherto the transfusion of blood from an animal of the same kind has been referred to, dog's blood injected into a dog. But when blood from a different species of' animal is used, there are frequently symptoms of poisoning developed. The urine is blood-coloured, and it contains albumen and tube casts; there is vomiting of bloody material, diarrhoea, etc. It is as if the foreign blood had acted as a poison, and we may inquire what is the nature of the poison. The observations of Ponfick and others have thrown considerable light on this matter. The urine is blood-coloured, but microscopic examination shows that this is due, not to the presence of red blood-corpuscles, but to that of the colouring matter of the blood in solution. It is not a bloody, but a blood-coloured urine; not a haematuria, but a Hemoglobinuria. The fact seems to be that there is no poison in the foreign blood plasma, but that the corpuscles are unable to survive in the alien blood; they dissolve, and their haemoglobin being dissolved in the plasma acts as a poison, and is eliminated by the kidneys. It seems to exercise its deleterious influence chiefly on the kidneys themselves, the tube casts and albumen in the urine being evidences of the irritation of these organs. The general symptoms, in fact, are largely referable to irritation of the kidneys.

If haemoglobin be introduced into the blood in other ways it acts equally as a poison. The red corpuscles of animals may be destroyed by repeatedly freezing and thawing the blood, and when that has been done, blood even of the same kind of animal will produce symptoms such as those referred to.

It is to be observed that all animals are not exactly in the same relation to each other in this respect. It is found, for instance, that a much smaller quantity of lamb's blood than of hen's blood produces hemoglobinuria in a dog. The importance of these facts in regard to transfusion in the human species will be apparent.

In this place it may be mentioned that the blood transfused does not, according to Panum, act as food or take its place. If an animal is undergoing starvation, transfusion does not avert or delay the process of inanition, it rather hastens it by increasing the waste. In using transfusion as a means of treatment the principal object is to make up the bulk of the blood, and this can be effected by the injection of serum or solution of common salt, with a small proportion of alkaline salt, making the solution near the specific gravity of the blood.

Plethora, as a pathological condition, is not of great importance. It may be presumed that in some persons the blood-forming organs, probably along with the other structures of the body, are unduly active in their nutritive processes. In that case there may be an excess of blood in the vascular system, which will manifest itself in an overful-ness of the capillaries and veins throughout the body, but especially in those of the abdominal viscera. Persons of vigorous digestion and active habits have often a florid appearance, as if the vessels, of the skin at least, were overfilled. The excess of blood is used, to a considerable extent, in the formation of fat, and we know that the subcutaneous adipose tissue and that of the abdomen are often much increased. But the observations mentioned above show that any excess of blood is disposed of with considerable rapidity, and we may infer that in the human subject a moderate tendency to plethora will be overcome. It will develop when the formation of blood keeps in advance of its destruction by the arrangements provided for that purpose.

The term hydrsemic plethora is used to designate a condition in which the quantity of the blood is in excess, but the corpuscles and dissolved constituents of the plasma are deficient. The blood is abundant, but watery. This, which is not a permanent or independent condition, is discussed in relation to oedema further on.

There may be a certain amount of plethora resulting from the stoppage of customary bleedings, as from piles, excessive menstruation, etc., and there will be a definite increase in the amount of blood relatively to the capacity of the vessels when, before amputation of a limb, its vessels are emptied into the circulation by the application of an elastic bandage.

We have again an increase in the total volume of the blood in cases where the capacity 6f the vascular system is increased. This occurs in many cases of disease of the heart, where not only the cavities of the heart are often greatly enlarged, but the capillaries and veins in the liver, iddneys, etc., are much dilated. Some of the symptoms in heart diseases may be due to difficulty in dealing with the increase of the mass of blood.

In new-born children there will frequently be a sudden increase of the mass of the blood. Before birth the foetal blood is divided between the child and the placenta. After the birth of the child, if the umbilical cord be not immediately ligatured, the contraction of the uterus will empty the fetal part of the placenta into the child. It has been estimated that this will sometimes amount to 100 grammes, or equal to one half the previous bulk of the blood. A portion of this blood will be accommodated in the lungs, which, on their inflation, increase the capacity of their vessels, but these will not always take up the whole excess. It is asserted by some that the common icterus of the new-born (see Icterus) is due to the disposal of the excess of red corpuscles.

Literature

Worm Muller, Transfusion u. Plethora, 1875; Panum, Virch. Archiv, vols, xxvii., xxix., and lxiii.; Ponfick, ibid., lxii.; Budin, Comptes Rendus 1876; Goltz, Virch. Archiv, vol. xxix.; Kronecker und Zander, Berl. klin. Wochensch, 1879, No. 52; Jennings, Transfusion of blood and saline fluids, 1888; Thoma, Path, and Path. Anat. (transl. Bruce), 1896.