The spleen is the largest of the ductless glands, and is situated in the left hypochondriac region. It is of a dark slate or bluish-gray color, and often of wrinkled appearance. It is of soft, friable structure. It rests between the stomach, diaphragm, and left kidney, and in form resembles a flattened oval. It extends from the level of the eleventh rib, beginning one or two centimeters distant from the vertebral column, downward and forward to a position about four centimeters from the point of the eleventh rib (Lushka). It is separated from the ninth, tenth, and eleventh ribs by the diaphragm. It presents two surfaces—one external and convex, facing the diaphragm; the other internal and concave, applied to the cardiac end of the stomach. The hilum divides the internal portion into two parts by a deep fissure, which marks the line of attachment of the gastro-splenic omentum. The larger and anterior part is bound to the fundus of the stomach by delicate areolar tissue, and the posterior and smaller portion to the left pillar of the diaphragm and the left suprarenal capsule. The upper portion is connected with the diaphragm by peritoneum forming a suspensory ligament. The bottom of the hilum is perforated by a number of openings for the transmission of blood-vessels, nerves, and lymphatics. The anterior border of the organ is notched and thinner than the posterior border. The pointed lower end touches the splenic flexure of the transverse colon and rests upon the costo-colic ligament. The spleen varies in size and weight within wide limits. Its average weight in adults is 250 grams, its length from 11 to 13 centimeters, and its thickness from 4 to 6 centimeters (Orth). Its volume is from 150 to 180 cubic centimeters. According to Gray, the proportionate weight of this organ to that of the whole body varies from 1:320 to 1:400, gradually diminishing until old age, when the proportion becomes as 1:700.
In the vicinity of the spleen are often found a number of small bodies similar to it in structure. These are known as accessory spleens, and are usually situated in the gastro-splenic or in the greater omentum. The attachments of the viscus are not very close, and much variation in size and position is possible.
Except at the hilum the peritoneum forms everywhere one of the coverings of the spleen. Its peculiar sheath or capsule is composed of fibro-elastic tissue of a whitish color, prolongations of which extend into the substance of the organ and form the trabeculæ that constitute its supporting framework and sheaths for blood-vessels and nerves. A close meshwork is thus created in which are contained the splenic vessels and pulp. This fibrous coat and these trabeculæ contain involuntary muscular fibres. These, with the elastic fibres, provide for the changes in size that the organ undergoes. When incised, the normal spleen presents a reddish-brown color, and its substance may be readily broken down with the finger into a pulp. This pulp consists of a mass of branched intercommunicating connective-tissue corpuscles of different sizes, within the substance of which remains of red blood-corpuscles may often be detected. The interstices of these cells are filled with blood. The very large splenic artery enters the spleen by numerous branches, ramifying within the trabecular sheaths and terminating in pencils of minute size.
The external coats of the smaller arteries are converted into lymphoid tissue, which, suddenly expanding here and there, forms the bodies known as the Malpighian follicles, which are supplied with capillary vessels, and which may often be distinguished by the naked eye as points of whitish color, sometimes attaining the size of pinheads. These small arteries end in capillaries, which, according to Müller, gradually lose their cylindrical character and emerge into a system of connective-tissue corpuscles, inosculating with the corpuscles of the splenic pulp in such a manner that the blood passes into the pulp-tissue freely, and is gradually brought to the veins by the transition of this tissue into that of the blood-vascular system. The splenic lymphatics originate in the arterial sheaths and in the trabeculæ. In the former case they accompany the blood-vessels; in the latter, they communicate with a superficial network in the corpuscle. All join at the hilum and enter the neighboring lymphatic glands. The splenic nerves are from the right and left semi-lunar ganglions and right pneumogastric nerve. They accompany the branches of the splenic artery, and have been traced deeply into the tissue of the organ.
It is perfectly established that under normal conditions the volume of the spleen may vary considerably, and especially during the act of digestion, and that this does not occur through simple engorgement of the vessels. The very important experiments of Roy show that, in cats and dogs at least, the splenic circulation does not depend upon the ordinary blood-pressure, but is carried on "chiefly, if not exclusively, by a rhythmic contraction of the muscles contained in the capsule and trabeculæ of the organ."1 This rhythmic contraction and expansion Roy observed to occur with great regularity at the rate of about sixty contractions an hour, with extremes of rapidity of rhythm of forty-six seconds for the most rapid and two minutes three seconds for the slowest. He also observed that stimulation of the central end of a cut sensory nerve, or of the medulla oblongata, or of the peripheral ends of both splanchnics and both vagi, causes a rapid contraction of the spleen. Unsatisfactory as is our knowledge of splenic physiology and of its exact relations to the maintenance of life (for that the spleen is not the seat of a peculiar and exclusive function has been demonstrated by the survival of individuals after extirpation of the organ), at present certain theories of its nature find pretty general acceptance. Thus, it is considered that in the lymphoid tissue of the blood-vessels and Malpighian corpuscles leucocytes are produced—that the cells of the splenic pulp appear to take red blood-corpuscles into their interior, where their disintegration takes place. There are not sufficient grounds for believing that in the spleen red blood-corpuscles are formed. Recent observations of Tizzoni, Crédé, and Zesas have led them to the conclusion that they are made in the spleen; but Bizzozero and others deny that this occurs except after serious hemorrhage.
1 Journal of Physiology, vol. iii., 3 and 4, p. 203.
It is impossible to detect by palpation any part of a healthy spleen. Its area may be approximately defined by percussion alone, though even by this method it is not always easy to determine its position and size. Loomis advises that the patient be placed upon his right side in order to facilitate the examination. The anterior border of the spleen is then "readily determined by the tympanitic resonance of the stomach and intestines. Inferiorly, where the organ comes into contact with the kidney, it is difficult, and often impossible, to determine its boundary. Its superior border corresponds to the line which marks the change from flatness to pulmonary resonance." The vagueness of these directions is necessitated by the difficulties of the subject, the splenic outlines being liable to frequent variations. Schuster and Mosler give excellent reasons for prosecuting the investigation with the patient in the right semi-supine position.
Acute Congestion of the Spleen.
Except within the physiological limits already referred to, acute congestion of the spleen never occurs as a primary process. Under pathological conditions it is known to take place under a great variety of circumstances, principally, however, in connection with those states of the system in which disease is supposed to depend upon some specific principle or germ. To a minor extent it is probable that splenic congestion accompanies nearly all febrile conditions, and from the border-lands of health to that highest and most intense degree of hyperæmia by which the organ acquires a volume and prominence that have caused it to be designated as acute splenic tumor, all gradations may be observed, though in many instances these may be so slight as to be incapable of recognition clinically, and are only brought to our knowledge through necroscopic examination. The congestion becomes most marked in the course of the acute specific fevers. In typhus and typhoid fevers, in small-pox, scarlatina, diphtheria, in epidemic cerebro-spinal meningitis, in acute tuberculosis, in erysipelas, puerperal fever, in conditions of blood-poisoning and in malarial fevers, more especially those of more severe type, it reaches its highest development. According to Friedreich, a form of pneumonia (differing from ordinary croupous pneumonia in its serpiginous course), acute coryza, and acute pharyngitis and tonsillitis are accompanied by enlargement of the spleen in consequence of the septic nature of these disorders. During the fever of secondary syphilis a splenic enlargement purely hyperæmic in character may sometimes be detected. Similar conditions are occasionally observed in a number of other affections. This tendency of the spleen to active congestion is to be accounted for by its peculiar anatomical structure, whereby unusual facilities for hyperæmia are afforded, more especially in the infective fevers, in the course of which the organic germs which are supposed to constitute their essential principles collect in the pulp, and by their accumulation and multiplication serve to excite a more or less intense determination of blood to the part, the organisms themselves being taken up by the leucocytes and connective-tissue corpuscles composing the pulp. We can thus account for the multitudes of these organisms to be found in the splenic pulp after various infective disorders, as in relapsing fever as observed by Ponfick, in pyæmia by Birch-Hirschfeld, and in splenic fever of animals by various observers. The less intense degrees of congestion occurring during the various specific fevers and in many simple febrile disturbances are usually so slight as not to attract attention. When the hyperæmia has been unduly prolonged, as more especially occurs as a result of chronic malarial poisoning, leucocythæmia, pseudo-leucocythæmia, or Hodgkin's disease, there is a well-pronounced tendency toward permanent structural changes and the development of hypertrophy.
SYMPTOMATOLOGY.—Milder degrees of congestion do not, generally, reveal their existence by symptoms, and those of more pronounced character give for the most part signs that are vague and nearly obscured by the more prominent features of the pathological processes that occasion or accompany the splenic changes. It may happen that acute splenic tumor of considerable size may be quite painless. It has been objected, indeed, that when pain accompanies splenic enlargements it is not attributable to any sensibility of the spleen itself, but to the participation of the investing peritoneum in the morbid action or to the dragging of the enlarged organ upon the parts with which it is connected (Mosler). Patients, however, will often complain of a dull, aching pain and a sensation of weight in the left hypochondrium. Occasionally, this pain may be severe and lancinating or may extend to the shoulder. Headache and various digestive disorders—anorexia, vomiting, flatulence, and diarrhoea—may prove distressing accompaniments. Other symptoms, such as melæna, voracious appetite, vertigo, extreme anæmia with its various concomitants, etc., belong rather to conditions of protracted congestion where new formation and true hypertrophy have been developed.