Some authorities class this organ with the ductless glands and others class it with the lymph-nodes. It is situated directly beneath the diaphragm, behind and to the left of the stomach, and is covered by peritoneum from which folds extend to the diaphragm, stomach, and left kidney, and help to hold the organ in place.
All attempts to show indispensable or important functions of the spleen have been unsuccessful. It may be removed from the body without serious injury to the animal. The most important facts known about the spleen are the slow expansion and contraction of the organ occurring during digestion. After a meal the spleen increases in size and reaches a maximum about the fifth hour of digestion. Then it slowly decreases to its former size.
The significance of this is not known.
In addition, Webster's Third New International Dictionary defines "spleen" as: the seat of emotions and passions; the source of laughter; any of various passions or emotions or their manifestations; violent mirth or merriment; laughter; a fit of anger, malice, or bad temper; a sudden impulse; caprice; a proud courageous impetuous temper; manly spirit; high-spiritedness; latent malevolence or spite; violent feelings of anger or spite especially when suddenly and explosively released; extreme lowness of spirit; depression; melancholy.
In his book "All About the Human Body" Bernard Glemser writes: For many centuries the spleen was considered to be the organ of bad temper. We still use the word to mean ill humor, peevish temper, or spite. Even today we know very little about the spleen. We can live without it quite comfortably. As far as I know, people who have had their spleens taken out are just as bad-tempered as they were before.
The spleen is fairly large; in a grown person it is about the size of the fist, and it is purplish-red in color. It holds a lot of blood, it acts as a blood reservoir, releasing blood when you need it - for example, when you cut yourself badly.
Its most important work will probably surprise you: it destroys red blood cells. This work is done by both the spleen and the liver. The reason why red blood cells must be destroyed is that they wear out in about thirty days. When they are worn out, your body destroys them and uses the materials from which they are made to help make new red cells. Every second, your spleen and your liver destroy about ten million worn-out red blood cells. These must be replaced, of course. Every second, therefore, about ten million new red blood cells come into existence.
This process goes on constantly.
The following exerpts come from the "Man in Structure & Function" by Fritz Kahn, M.D.: The spleen is not a digestive organ although it lies next to the stomach. It has no relation to any neighboring organ, but is attached exclusively to the blood-stream. It could just as well be situated in some other part of the body.
The functions of the spleen are not yet known in detail. However, it does play a large role in blood formation during childhood, in fighting blood and bone-marrow diseases. On the other hand, however, it can be removed without interfering with the vital processes of the body, because it can apparently be replaced by other parts of the lymphatic system.
A remark made a century ago by a well-known physiologist is still true: It is one of the most obscure and mysterious corners of the human organism. In the same connection, the following occurrence during an examination of a medical student could still bear repetition at present: The professor requested the student to name the functions of the spleen. The latter hemmed and hawed, muttered a few words, then said: "Yesterday I knew them all, but now I have forgotten everything." "How unfortunate!" remarked the professor; "here we finally have someone who knows something about the spleen, and now this one person forgets it!"