they feed by engulfing their prey. This fact has a very important bearing on the relation of colorless corpuscles to certain diseases caused by bacteria within the body. If, for example, a cut becomes infected by bacteria, inflammation may set in. The bacteria form a poison known as a toxin, which causes this inflammation in their immediate neighborhood. Colorless corpuscles at once surround the spot and attack the bacteria. If the bacteria are few in number, they are quickly eaten by the colorless corpuscles, which are known as phagocytes. If bacteria are present in great Diagram showing how colorless corpuscles pass between the cells that form the walls of the capillaries; 1, 2, 3, 4, different stages. Hall. quantities, they may prevail and kill the phagocytes by poisoning them. The dead bodies of the phagocytes thus killed are seen in the pus, or matter which accumulates in infected wounds. In such an event, we must come to the aid of the colorless corpuscle by washing the wound with some antiseptic, as weak carbolic acid or hydrogen peroxide. NUMBER AND MANUFACTURE OF COLORLESS CORPUSCLES.-The number of colorless corpuscles, although normally about 17,000 to a drop of blood, may vary, especially in certain diseases. They are formed in large numbers within the lymph glands (collections of cells which are found here and there along the course of the lymph vessels). The spleen, which is somewhat like a lymph gland in structure, is also believed to manufacture colorless corpuscles. The Amount of Blood and its Distribution. Protoplasm of the body, as we know, is composed largely of water. The blood forms, by weight, about one thirteenth of the body. Its distribution varies somewhat according to the position assumed by the body, and the amount of undigested food in the stomach and intestines. Normally, about one half of the blood of the body is found in or near the organs lying in the body cavity, about one fourth in the muscles, and the rest in the heart, lungs, large arteries, and veins. Blood Temperature. The temperature of blood in the human body is normally about 98.5° Fahrenheit, although the temperature drops almost two degrees after we have gone to sleep at night. It is highest about 5 P.M. and lowest about 4 A.M. Any considerable variation in the temperature of the blood means death. In fevers, the temperature of the body sometimes rises to 107°; but unless this temperature is soon reduced, death follows. Any considerable drop in temperature below the normal also would mean death. Bodily temperature, as we know, results from the oxidation of food; to a great degree, the oxidation of fatty foods in the blood within the lungs. Cold-blooded Animals. In lower animals which are called cold blooded, the blood has no fixed temperature, but varies with the temperature of the medium in which the animal lives. Frogs, in the summer, may sit for hours in water with a temperature of almost 100°. In winter, they often endure freezing so that the blood and lymph within the spaces under the loose skin are frozen into ice crystals. Such frogs, if thawed out carefully, will live. This change in body temperature is evidently an adaptation to the mode of life. Necessity of Good Food, Fresh Air, and Sleep. - Inasmuch as the fluid part of the blood receives its nourishment directly from the foods which are taken into the body, it follows that if food materials contain an ill-balanced proportion of nutrients, the blood and the body may suffer. Proteid food must be taken into the blood at all times, for without proteid, no protoplasm can be formed. Plenty of nourishing food is essential. The red corpuscles, which have the important function of carrying the oxygen, must be kept in healthy condition. To do this, plenty of fresh air is absolutely essential. Sleep also seems to be a necessary factor in the health of the red corpuscle. Many are familiar with the pale face which comes from sleeplessness and overwork in poorly ventilated rooms. Moderate exercise is another important factor. The disease called anæmia, which means a lack of red corpuscles in the blood, is too often brought about by sedentary habits and lack of sleep and air. Tonics containing iron are given in such cases so as to supply the lacking element to the hæmoglobin of the red corpuscle. CAT. A. XXX. CIRCULATION The Organs of Circulation in the Frog.· In a frog that has been recently killed the organs of circulation may be made out in part. It is best, however, to have a specimen in which the blood vessels have been injected with some semifluid mass (made of gelatine or starch colored with carmine or other bright coloring material). Two specimens should be used to demonstrate the organs of circulation, one for the veins, the other for the arteries. In a specimen killed by chloroforming find the nearly triangular-shaped heart. It is seen to be composed of two distinct parts. a light-colored area, the ventricle, and a broader portion, which is darker in color. This latter area is made up of the two auricles. Compare the two areas of the heart in position. The auricles, according to their position, are called respectively the right and left auricles. D.T.A. V.H. -D. A. R.A. -TL. P.A. The arterial system of the frog may be said to include all blood vessels which carry blood away from the heart. The heart is only imperfectly divided into a right and a left heart, there being only one ventricle, with an imperfect partition wall extending in an anterior-posterior direction. Blood leaves the heart to pass to the lungs by a vessel (shown in the diagram), known as the pulmo-cutaneous trunk, because it carries blood to the skin and lungs. Over the ventral surface of the heart is found a large common trunk, the conus. This divides into two branches while still over the heart, and then each branch splits into three large arteries, the carotid, systemic, and pulmo-cutaneous appearing from the midline as we go outwards. Trace the course of the carotid artery; it supplies the head and neck with arterial blood. The systemic arteries are the most important in the body. Trace one backward to where it unites with its neighbor on the opposite side of the body to form the dorsal aorta, the great main trunk supplying the organs of the body cavity and the muscles of the body and legs. Find the branches passing to the stomach, intestine, liver, and other organs held in the mesentery. Farther back, arteries may be found that pass to the kidneys and genital organs. The aorta divides to form two large trunks, the iliac arteries, that supply the muscles of the hind legs. Make a drawing to show the principal arteries and their connection with the heart of the frog. Arterial system of the frog; The system of blood vessels which return blood from the various organs of the body to the heart is known collectively as the venous system or veins. Pr. CV. P.V. In the frog some of these blood vessels are somewhat difficult to find; others may easily be seen. One which collects blood from the skin and muscles near the ventral surface of the body, but chiefly from the hind legs, is called the abdominal vein. It may be seen near the surface, on the ventral midline of the body, as we open the frog from the ventral side. This vein turns inward at a point nearly between the fore limbs, divides into two branches, and enters the liver. Just before it reaches the liver, another vein, bringing blood from the digestive tract, joins with it. The rest of the blood from the hind legs has to pass through what is known as the renal portal system of circulation, the veins of which send the blood through the kidney, and thence, by a large single vein (the postcaval vein) to a thin-walled sac on the dorsal side of the heart. This sac, known as the sinus venosus, receives the blood from the veins and empties it into the heart. Immediately before reaching the sinus, the blood from the liver (the so-called portal circulation) joins with the postcaval vein. It is seen in the portal circulation that part of the blood of the body passes through the liver before reaching the heart. Blood from the head region is returned to the heart by two large precaval veins. The blood from the fore limbs also takes this course. R. Pt. CV. V R K. R.P abd Sc.V fr Venous system of the frog; a.b.d., abdominal vein; f.r., femoral vein; H, heart; L, lungs; K, kidney; LIV., liver; P. V., pulmonary vein; Pr. CV.V., precaval vein; R., R., renal veins; SV, sinus venosus; Sc. V., sciatic veins. (After Parker and Haswell.) Circulation of the Blood in Man. As in the frog and other vertebrate animals, the organs of circulation are the heart and blood vessels. These blood vessels are called arteries when they carry blood away from the heart, veins when they bring blood back to the heart, and capillaries when they connect the arteries with the veins. Except in the spleen, where the blood capillaries are open, blood flowing between and around the cells, the organs of circulation form a system of closed tubes through which the blood flows in a continuous stream. The Heart; Position, Size, Protection.-The heart is a coneshaped muscular organ about the size of a man's fist. It is located immediately above the diaphragm, and lies so that the muscular apex, which points downward, moves in beating or contracting against the fifth and sixth ribs, just a little to the left of the midline of the body. This fact gives rise to the notion that the heart is on the left side of the body. The heart is surrounded by a loose |