In all the medical schools of London a notice is posted over the door leading to the dissecting room forbidding strangers to enter. I propose, however, to push the door open and ask the reader to accompany me within, for, if we are to understand the human body, it is essential that we should see the students at work. If we enter in the right spirit—with a desire to learn something of the structure of man's wonderful body with our own eyes—there is nothing in the room which need repel or offend us. The room is lofty, well-lighted and clean; the students in their white coats are grouped round tables on which lie the embalmed bodies of men and women who have run the race of life—often, alas 1 with but ill fortune. The students are dissecting systematically, each with his text-book placed beside him for consultation and guidance, and with the instruments of dissection in his hands. The human body is to be the subject of their life's work ; if they are to recognize and treat its illnesses and injuries they must know each part as familiarly as the pianist knows the notes of the keyboard. We propose to watch them at work. Each student is at his allotted part, and if we observe them in turn we shall, in an hour or less, obtain an idea of the main tissues and structures which enter into the composition of the human body.
By good fortune a dissection is in progress in front of the wrist, which displays, amongst other structures, the radial artery at which the physician feels the pulse and counts the rate of the heart's beat. The skin here is loose and thin, and as the student turns it aside in flaps he uses his knife to free it from the white subcutaneous tissue which binds it down to the deeper parts. He looks at his own wrist and sees why the skin here is loose ; as he bends his wrist the skin is thrown into folds; when he extends it, the skin in front of the wrist is stretched ; unless it were loosely bound down it would be impossible to move the wrist joint freely. On the palm the skin is different; it is thick and bound firmly by dense subcutaneous tissue to the underlying parts; there would be no firmness of grasp unless the skin of the palm were thick and closely bound down. As the student turns back the skin from the front of the wrist he searches in the loose tissue under it for the nerves which supply the skin with the power of feeling and for small veins which carry the used or venous blood back to the heart. He squeezes the blood backwards in these vessels; they swell out here and there into little knobs owing to the presence of pockets or valves which permit the blood to flow only in one direction, namely, towards the heart. It was the study of the arrangement of these valves, nearly three centuries ago now, which led Harvey to the discovery of the circulation. Beneath the skin and subcutaneous tissue there is another covering which has to be cut through before the sinews or tendons in front of the wrist are exposed to view. This third wrapping—the deep fascia the student will call it—is membranous and strong and keeps the tendons in place; workmen often find it necessary to add additional support by means of a wrist-strap. The tendons are glistening almost white ; eight of them go to the fingers (two to each); one goes to the thumb and two act on the bones of the wrist or carpus. Just above the wrist joint the tendons have attached to them the muscles which flex the fingers and the wrist. They look so simple in the dead body; yet one has but to watch the fingers and wrists of the pianist or of the typist to see how quick and complicated they can be in life. As the student traces the tendons into the palm of the hand he sees them become infolded within a loose sac with its interior lined by a smooth lubricated surface. This synovial sac is an example of the perfect manner in which the human machine is made; a self-oiling mechanism is provided at each point of friction. From overwork or injury fluid may collect in this sac and weaken the power of the workman's wrist.
Lying side by side with the sinews at the wrist there is another cord, somewhat like them in appearance, but very different in nature. It is the median nerve. Our friend the dissector has already seen a patient in the wards of the hospital with a jagged wound at the wrist which has injured the nerve. In that case he noticed that the thumb, fore, middle and part of the ring fingers had lost their usual sense of feeling, and that some of the small muscles of the thumb had no longer the power of movement. For our benefit he traces the nerve upwards in the forearm, arm, through the armpit until it reaches the root of the neck, where it is seen to be formed by five pairs of nerve roots which issue from the spinal cord. In the median nerve we see one of the paths which unite the brain and hand ; messages pass by it from the hand which the brain interprets as heat or cold, rough or smooth, sharp or blunt; other messages pass outwards from the brain to start or stop the muscles of the forearm or fingers. The student pays particular attention to the radial artery ; on the wrist, just above the root of the thumb, he finds the vessel resting on the lower end of the radius. He places his finger over the artery and observes how easily he can press it against the bone. In life we feel the artery suddenly expand and then subside with each beat of the heart; with a finger on the pulse the physician knows how the heart is working.
We propose to observe the dissector as he traces the radial artery to the heart. Below the bend of the elbow it is seen to issue from the main vessel of the upper arm—the brachial; the brachial in turn is found to be a continuation of the great artery of the armpit—the axillary. From the armpit the great arterial channel is followed across the root of the neck through the upper opening of the chest or thorax until it joins the aorta—the great vessel which springs from the left ventricle of the heart.
It must not be thought that the artery at the wrist is merely an elastic-walled pipe which expands passively as the ventricle discharges its load of blood; it is much more than that. When the student places a very thin section of the artery under the microscope for our particular benefit, we see that it has an exceedingly smooth lining, in order that the blood may flow with a minimum of friction ; outside the lining there is seen an inner coat which contains many elastic fibres; then another coat made up of small contractile or muscular fibres. These muscular fibres regulate the size of the artery; they give or yield with each beat of the heart, and then contract, thus assisting the heart to force the blood onwards to nourish the tissues of the hand. The artery we have just seen under the microscope had been continuously expanding and contracting for over seventy years at the rate of seventy or eighty times a minute. No elastic tube yet invented by man could have done that. We note, however, that it has suffered the changes which overtake our arteries when they have been at work for forty years or even less; the elastic tissue and the muscle fibres are clogged with lime-salts; the elasticity of youth is gone. Hence as we grow older we cannot make the violent " spurts " of our youth.