deoxygenated state than from a muscle, or from the brain. The blood of the renal veins is not like ordinary venous blood, but bright red, like arterial blood; and, in correspondence with the fact that the kidney separates urea from the blood, its venous blood contains less urea than other venous or than arterial blood. Other glands which are sometimes in action, sometimes at rest, show corresponding differences the venous blood of the submaxillary gland, which is of the usual venous quality while the gland is at rest, becomes bright red, like arterial blood, while the gland is actively secreting. With muscles the reverse is the case: under ordinary conditions their venous blood is of the ordinary typical venous quality, but if it is analysed for gases during muscular activity, it is found to be more venous than before, and both the deficit of oxygen and the excess of carbonic acid are greater than in the blood coming from quiet muscles. From paralysed muscles the blood is, on the contrary, less venous, and both the deficit of oxygen and the excess of carbonic acid are less than before. Differences of temperature also obtain in different kinds of venous blood; venous blood returning in a superficial vein from an external part, is cooler than the arterial blood going to the part; thus, for instance, blood in the jugular vein is of lower temperature than in the carotid artery, and the blood in the crural vein is about 1° lower than that in the crural artery.' On the other hand, deep veins leading from active organs contain blood at a higher temperature even than that of arterial blood; of this inequality the hepatic venous blood is the best known instance-its temperature is about 1° higher than that of the blood in the aorta. The blood of the splenic vein contains a larger proportion of leucocytes than normal blood, in consequence of the production of leucocytes taking place in the gland.

Composition of the blood in disease.-Anemia, or poverty of the blood, is the commonest and most widespread departure from the healthy standard, and is the invariable consequence of copious bleeding or of any kind of prolonged or debilitating disease. The popular term 'poverty of the blood' is accurately descriptive; the blood of an anæmic person is not deficient in amount, but it is a weak blood, with an excess of water, and a deficiency of solids, and a low specific gravity; the number of red corpuscles is deficient, and the amount of hæmoglobin in these even is deficient; contrasting the blood of a healthy person

The Centigrade scale will always be referred to in the text. The relation between the Fahrenheit and Centigrade scales is given in the Appendix.

with that of a patient in extreme anæmia, there have been found. for instance: :

from which it is evident that the deficiency is essentially a deficiency of hæmoglobin.

Leucocythemia is a state characterised by an excessive number of leucocytes in the blood, and is usually associated with excessive growth of the spleen, or of the lymphatic glands.

According to observations made in the old blood-letting days, the blood of a person suffering from severe inflammation (of the lung, for instance) usually yields an excessive amount of fibrin, but coagulates more slowly, with formation of the so-called buffy or inflammatory coat.

Diseases of the kidneys are accompanied with anæmia, and the blood contains an excess of urea. In gout, the function of the kidneys is generally deficient, and the blood is consequently altered as just stated, with this additional and characteristic feature, viz. excess of uric acid.

Diseases of the liver very commonly cause anæmia; when the flow of bile is obstructed, bile-pigment accumulates in the blood and lymph.

The blood of patients suffering from severe diabetes contains an excess of sugar.

Hemophilia is the name applied to a condition in which there is a peculiar tendency to bleeding, which it is difficult to check. The blood of persons subject to this affection is said to be deficient in fibrin.

Quantity of blood in the body. The total amount of blood has been estimated to be in man about of the body-weight, i.e. five to six litres (or rather more than one gallon). From this datum, and from those given on page 13, we may form a rough notion of the absolute amounts of the various proximate principles in circulation in the blood, viz. about 500 grammes hæmoglobin, 450 grammes proteids, 2.5 grammes iron, &c.

The total amount is distributed in the body approximately as follows in the thoracic viscera in the muscles; in the liver; in remaining parts. It is estimated by collecting

all the blood that escapes when an animal is bled to death, subsequently washing out the vessels with salt solution, finally mincing and washing the organs. The amount of blood in these two washings is found by comparison of their red tint with the tint of a sample of blood of known dilution; the comparison is facilitated by the previous passage of carbonic oxide through the fluids. For example, a dog weighing ten kilogrammes is bled, and yields 400 c.c. of blood; the vessels are washed out and the various tissues are minced and washed; the united bulk of the washings is five litres, and the tint is found to be equal to that of one c.c. of blood fifty times diluted, i.e. the five litres contain of blood 100 c.c. The total amount of blood is therefore 500 c.c., that is to say, the weight of the dog.

The estimation of the blood in particular organs is determined in a similar manner, the vessels having been previously ligatured before the cessation of circulation.

Tests for blood.-It is often required to determine whether or no a pathological fluid contains blood-whether or no a stain on weapons or clothes is due to blood. We have four tests by which blood may be identified. (1) By the microscope we may determine the presence or absence of blood-corpuscles in a fluid or in a fresh stain. We may be able to determine whether the blood is mammalian or that of a bird or fish, but we cannot specify what kind of mammalian animal is the source of the blood under examination. There are, it is true, differences of size between the red corpuscles of various mammalia (ride fig. 3), and we might thus, for instance, be able to deny that a stain caused by goat's blood was caused by human blood, but we should not be able in practice to distinguish human blood from that of animals such as the cat, dog, rabbit, ox, &c. On the other hand, we might positively distinguish the blood of fowl or fish from that of mammalia. A knife stained with blood containing oval corpuscles has, in all probability, not served to kill a man; a girl supposed to spit blood which is found to contain oval blood-corpuscles has probably obtained it from a fowl, and is certainly attempting to mislead.

In many cases corpuscles may not be found and yet blood be present; it will, however, be identified by other tests, which, indeed, are in all cases to be employed as confirmatory tests. Of these the best is (2) the hamin test, applied as above stated; the presence of hæmin crystals proves the presence of blood, but gives no information as to its kind; any kind of blood can

yield hæmin crystals, and a blood-stain, however old, will yield them.

(3) The spectroscope affords a convenient and expeditious means of ascertaining whether or no a coloured fluid owes its colour to blood. The fluid may contain hæmoglobin or its derivatives. An ordinary blood-stain dissolved in water gives the oxyhæmoglobin spectrum, or, if old, it may give the methæmoglobin or the hæmatin spectrum: the blood of a person poisoned by coal-gas will give the carboxyhæmoglobin spectrum: blood in the urine, or in the vomited contents of the stomach, may give either the oxyhæmoglobin, the methæmoglobin, or the hæmatin spectrum. These will be distinguished as above decribed, and by the alterations effected by reducing agents. It is of practical importance to remember that the spectrum of oxygenated hæmatin is much less distinct than that of reduced hematin; so much so that a pathological fluid containing hematin may yield a blank spectrum until after the addition of ammonium sulphide. It is also to be borne in mind that the hurried examination of a pink fluid and the discovery of a two-banded spectrum are not proof positive that hæmoglobin is the colouring agent, for carmine gives a very similar spectrum. If a very small quantity of fluid is available, the spectroscope is used in combination with a microscope, being substituted for the eye-piece of the latter an instrument of this kind is termed a microspectro

scope.

(4) On the addition of fresh tincture of guaiacum and ozonic ether (which contains hydrogen peroxide) to a fluid which contains a trace of blood, a sapphire-blue colour is produced. The test is, however, not characteristic, for blood is not the only substance by which the colour is elicited.

42 General principles: Course of the blood-Systemic vessels-Pulmonary vessels - Valves-Rhythm of the heart's action-Cardiac cycle-Systole and diastole-Blood-pressure-Nervous mechanism.

46 Physiological anatomy of the heart.-Inflamed pericardium-Pericardial friction-Pericardial effusion-Relation between bulk and work-Hypertrophy-Structure of the frog's heart.

49 Examination of the human heart: Percussion--Auscultation-The cardiograph-Duration of systole and of diastole.

55 Blood-pressure: In the arteries-The factors of blood-pressure-The manometer-Tension '-Variations of blood-pressure and of blood-flow-Local and general variations Effects of addition and removal of blood --Bloodpressure in the capillaries, in the veins, and in the heart - Influence of varying arterial pressure upon venous and upon pulmonary pressure. 66 *Further physical considerations: Velocity and pressure-Instruments used -Stromuhr-Tachometer-Dromometer-The time of circulation --The capacity of the ventricles-The work of the heart- Elasticity-curves of blood-vessels-The plethysmograph-The oncometer -The cardiometer The sphygmomanometer.

80 The pulse: Frequency -Compressibility-Venous pulse-Capillary pulse The Sphygmograph: Marey's instrument-Its value-The normal pulsetracing-High-tension pulse-Low-tension pulse-Nature of the dicrotic wave-Velocity of the pulse.

88 *On the properties and mode of contraction of cardiac muscle: Excised heart-Ventricle-apex-Ventricle-strip-The coronary arteries- Stannius' experiments-1st ligature -2nd ligature-Experiments on Stanniused hearts All or nothing'-The staircase -The refractory period- Tetanus? -The wave of contraction-Blocking '-Influence of temperature.

95 *Drugs by which the action and properties of the heart can be modified: Muscarin-Pilocarpin-Atropin-Antagonism of muscarin by atropinNicotin Physostigmin - Curare-Digitalin - Veratrin Aconitin Alcohol-Chloroform and ether-Neutral salts-Nutritive fluids.

99 *Influence of the nervous system upon the heart and upon the blood-vessels: Physiological anatomy of cardiac nerves-Physiological anatomy of vaso

motor nerves.

102 The vagus: Effect of division and of excitation-Inhibition-Latent period and duration of vagus action-After-effects-Successive stimulation of both vagi-The spinal accessory-Inhibition on man-Action of vagus post mortem-Reflex inhibition-Fainting-Expiratory slowing- Swallowing- The trophic' theory-The accelerator nerves.

107 Vasomotor nerves: Constrictors and dilatators-Cervical sympathetic of rabbit, and chorda tympani of dog-Nerves of the limbs-The splanchnic nerves-Nervi erigentes-Muscular nerves-The dog's mouth-Pulmonary vasomotor nerves ?-The vasomotor centre: Destruction and excitation of spinal bulb-The depressor' nerve: Exceptional effects-Local vasomotor reflexes.

115 The lymph circulation: Lymph-hearts-Lymphatic glands-The secretion of lymph.