Part 13

Another anomalous example of the function of this tissue is found in the hematopoiesis of birds. While there seems to be some evidence that in the spleen and liver red blood cells may be formed, there is perhaps at most times sufficient bone marrow to keep the blood cells at a proper number. There is no inverse relation between the amount of bone marrow and that of splenic bulk; that is in diving birds with their hollow bones the latter is no greater than in gallinaceous birds which have abundant marrow in all the skeleton.

It has been suggested that the spleen supplies an activator for pancreatic ferments. This receives a sort of support from the greater size of the organ in carnivores and smaller relative size in ungulates, since in the former concentrations of digestive enzymes are more often needed. Because of the greater excretion of iron in splenectomized animals or those being starved, Fischer has thought that the spleen has some power to metabolize this element; this receives some support from the statements concerning the size of this organ in the carnivorous orders. From experimental studies it appears that some relation exists between the lymphocytes and resistance to implanted tumors. If one apply this idea to the amount of lymphatic tissue and the incidence of spontaneous new growths, it is found that no definite relationship is discoverable either in terms of size of spleen or richness in lymphatic nodes. Carnivores, rodents and marsupials show a high tumor incidence and have a good lymphatic supply. Aves, on the other hand, with a poor nodal apparatus and a variable splenic bulk, show many fewer tumors than do the mammals. The mononuclears of avian blood rise normally as high as 60 per cent., of which 40–45 per cent. are of the small size.

The size of the spleen is subject to great variation not only within orders but actually within genera; it even seems that one sometimes sees two or three members of a species kept in the same enclosure, maybe with the same disease, maybe without any obvious disease, yet with definite variation in the size of the organ. This irregularity is recognized by veterinarians (Hutyra and Marek) who ascribe it to some unknown disease, past or present, and to normal variation. The lack of uniformity is seen more clearly in birds than mammals. In the former it might be due at times to low grade or inactive parasitism or, conjecturally, to toxins from incorrect diet; we shall see later that infection and intoxication seem to have a different effect. Some writers have mentioned the possibility of an idiopathic splenomegaly (?), a condition associated in youthful human beings, with anemia and lymphadenopathy, and occasionally going over into a sort of leucemia. The existence of such a condition is difficult to admit or deny; we have met nothing which could not be aligned in some fairly well defined group. Birds have a relatively larger spleen than mammals and in addition the organ seems to respond more actively in infections or intoxications, since it may reach, under active stimulation, a size ten times that of the normal organ.

ENLARGEMENTS OF SPLEEN.

Acute enlargements of the spleen, be they of congestive or “inflammatory” nature are quite common among the lower animals, a fact that is recognized in veterinary medicine. Congestions of the spleen are most often seen during acute infections and diseases of the heart and liver. The diagnosis has been made among mammals proportionately more than in birds, 27 or 1.5 per cent. to 35 to 1 per cent.

REASON FOR CONGESTIVE ENLARGEMENTS.

Perhaps this is partly due to the circulatory anatomy since in the former the arterial and venous supply is usually by one large vessel of each kind, whereas in birds the splenic branch of the cœliac axis breaks up into several small arteries and the venous return is accomplished by numerous venules some of which reënter the posterior cava almost directly, others joining with the mesenteric to form the portal; by this arrangement a more elastic system is assured. The same condition is found when analyzing the records of chronic passive congestion; in eighteen recorded cases, fourteen were mammals and four birds. In these cases the principal associated pathological lesions were pleural and pulmonary in seven, cardiac in three, renal in three and hepatic in four. While the anatomy of the splenic blood supply may help to explain the small number of congestions in Aves, it will not answer for the inflammations which occur in large numbers in this class; this will be discussed in the following pages.

Hemorrhage and infarction of the spleen are not very common, there being eleven of the former and ten of the latter and all occurring with the same indication or history of infectious disease; in one case, an opossum (_Didelphys virginiana_) an injury probably caused a massive hemorrhage shaped like an infarct. It is, however, curious that of the twenty-one cases only five occurred in birds, of which only one hemorrhage was in the shape to which the term infarction is best applied. There have been, as one might expect, a few cases of infected infarction, with abscess. It is perhaps worth noting that no case of hemorrhagic cyst or inspissated coagulum has been seen. Only one case of rupture is recorded secondary to acute splenitis during an acute septicemia.

INFLAMMATIONS.

It has been the practice at this laboratory to classify splenitis in three ways, (1) acute diffuse splenitis—general congestion with perhaps small hemorrhages, swelling but retention of general architecture and with no undue prominence of the follicles; (2) follicular hyperplasia— where this is the prominent gross and minute finding, the pulp being less pronouncedly involved; (3) acute splenic tumor—where the organ is greatly enlarged but with loss of the usual markings. Perhaps this separation is not warranted upon a strict etiological basis, and yet as we shall see it holds true fairly well in the toxic and infectious lesions. Moreover, from the following list it is evident how the various orders call upon the splenic tissue in disease.

TABLE 7. _This Shows the Percentage of Various Forms of Splenitis in the Animals Coming to Autopsy._ ═════════════════╤═════════════════╤═════════════════╤═════════════════ │ Acute Diffuse │ Follicular │ Acute Splenic │ Splenitis. Per │ Splenitis. Per │Tumor. Per cent. │ cent. │ cent. │ ─────────────────┼─────────────────┼─────────────────┼───────────────── Carnivora │ 7.│ 3.│ 1.3 Primates │ 2.5│ 4.9│ 2. Ungulata │ 2.4│ .3│ 1.2 Rodentia │ 2.6│ 4.7│ 1. Marsupialia │ 9.2│ 3.│ 3.7 Pinnipedia │ _33._│ │ Proboscidea. │ _33._│ │ Edentata │ _12.5_│ │ _6.2_ │ │ │ Passeres │ 3.│ 3.│ 3.8 Psittaci │ 6.5│ 2.3│ 4.1 Anseres │ 5.2│ 7.2│ 5.2 Herodiones │ _1._│ _6._│ _2._ Galli │ 2.6│ 1.5│ 4.7 Struthiones │ _10._│ _10._│ _1._ Accipitres │ 7.5│ 3.7│ 1.6 Gaviæ │ │ │ _5._ Picariæ │ _4._│ │ _1.3_ Striges │ 6.8│ 3.4│ Fulicariæ │ _3._│ 6.│ Steganopodes │ │ _10._│ Columbæ │ .7│ .7│ ─────────────────┴─────────────────┴─────────────────┴───────────────── For the meaning of italics see foot note Table 1.

The points to draw from this chart are first the greater variety of lesions seen in the birds, which apparently make greater use of the organ in defence, and the preponderance of acute diffuse hyperplasias in mammals. It is noteworthy that the Primates and Marsupialia show more of the acute hypertrophy of the spleen going under the name of tumor. It would be interesting and valuable to be able to discover exactly what determines and constitutes the conditions usually termed hyperplasia and inflammation of the spleen and an attempt was made in this direction by tabulating the data from Table 7 in terms of each diagnosis, classifying these latter also as infectious and toxic. The results of this effort are not conclusive, and while they permit of some discussion of the lesions, do not allow finished conclusions. The figures obtained by study are not illuminating. One can state, however, that in infections, either specific or not specific, more elements of the spleen were engaged in the process than when the condition did not resemble a communicable disease, but might be called toxic. Under the former condition the diagnosis of splenitis or acute tumor predominated, while under the latter follicular hyperplasia is more often recorded. Anatomical alterations in these two groups are described in the definition given in a previous paragraph and deserve no special discussion except in so far as they concern the changes in the avian splenic tumor when under magnification.

Microscopically there is a total loss of the relations in the acute splenic tumor of birds, the chords and follicles being replaced by a rather regularly arranged mass of small and large mononuclears, granular cells of the circulating types and red blood cells; pigment always seems increased. Endothelial cells do not take part in the general mass of the organ but along lymph and blood vessels their bulk and number are increased so that if the packing be not too dense one may find double lines of these cells passing through the hyperplastic tissue. There is, however, a group of seven cases (six birds) to which the term endothelial hyperplasia in the spleen has been applied. All of them show an unusual prominence of the vascular linings and of the follicular centres and perivascular areas; besides this there is a moderate general hyperplasia. An examination of the history and autopsy results in the birds indicated that they had all suffered with some rather protracted intoxication and showed a moderate anemia (four of the spleens were well pigmented).

The more chronic changes of this organ, be they moderate or of a grade to which one must apply the term fibrosis, are rather uncommon when one considers the number of animals with prolonged infection, anemia, skeletal diseases and hepatic cirrhoses; these are the conditions that take a prominent place in the associated pathology and history. There is no essential difference in the organ throughout the animal kingdom, and one may find as far down as the struthious birds analogies to the processes of domestic and human animals.

SPECIAL SUBJECTS—AMYLOID.

Amyloid changes in the spleen have occurred in the following orders: Primates, Carnivora, Rodentia, Marsupialia, Passeres, Galli, Gaviæ, and Anseres, fourteen cases in all. This infiltration is usually ascribed to long continued suppuration or chronic infection, every one admitting, however, that once in a great while a case is seen wherein no cause can be discovered. In this laboratory we have a high percentage of cases without adequate accompanying pathology so that we have called six of the above cases primary or idiopathic. The gross appearance of the spleen is in all these cases that of an enlarged, firm, homogeneous body without the sago spots usually described for this change. Microscopically the infiltration occurs first in the vessel walls, thence spreading to the sinus walls and reticulum. Joest in discussing this infiltration[19], states that it is comparatively rare among the domestic animals, where it may appear under the usual conditions or as a primary affection; it seems at times to follow unsuitable feeding. According to this author, the “sago” type is more common than the “bacony;” this has not been our experience. The most conspicuous example is given here.

European Badger (_Meles meles_) Adult ♀ . Gradual failure for two weeks.

DIAGNOSIS.—Amyloidosis. Chronic parenchymatous nephritis. Emphysema of lungs.

Muscles atrophic; fat scanty. Heart is dilated and muscle is red- brown. Aorta is jaundiced and there is a small patch of atheroma near the anterior leaflet of aortic valve and about 5 mm. above it. Abdomen contains a slight amount of clear fluid, no adhesions. Liver is normal in size, smooth surface, sharp edges, firm consistency, yellow color. The section surface is glistening, smooth and moist. The spleen is very hard, greatly enlarged (25 × 6 × 2 cm.) and lies across the abdomen over the intestines. It is pale red and very bacony. In iodin the tissue stains a mahogany brown. The kidney is normal in size. (5½ x 3 cm.). The capsule is smooth and strips easily leaving a smooth, yellow surface. Organ is firm. The section surface is glistening, has a relatively narrowed cortex and relatively wide medulla. The glomeruli are barely visible but stain a mahogany brown in iodin. The adrenals are 12 × 10 × 4 mm. The cortex is wide, dull yellow and regular. The zone beneath fades into the cortex although rather abruptly. The centre of both glands is occupied by an irregular pale yellow, sharply outlined nodule suggestive of solid medulla, tubercle or tumor. The zone between cortex and this is gray, irregular and firm. This is practically a normal figuration. The stomach is empty, mucosa apparently normal. Intestines were not opened but serosa seems normal; when opened after Kaiserling fixation they seem normal. The pancreas is normal in size, firm and pale. Lymphatics of the mesentery are slightly enlarged, soft, homogeneous pale yellow.

HISTOLOGICAL NOTES.—Lung seems somewhat atrophic and there are some vesicular ruptures. One small patch of amyloid found in blood vessel wall. Liver shows slight capillary congestion and granularity of parenchyma. There is a marked blood vessel amyloid deposit not only in interlobular spaces but in intralobular capillaries. Spleen, no trace of splenic tissue recognizable in section. It is composed of more or less eosin-staining material surrounding single, or small collections of round or plasma cells. Kidney shows marked amyloidosis of glomeruli and slight deposit in blood vessel walls and in the increased connective tissue. There is a general moderate fibrosis; irregular tubules; low epithelium and hyaline casts. Heart muscle fibres are small and stain deeply. No amyloid in section. No pigmentation although section is suggestive of brown atrophy. Adrenal is practically negative. There seems to be slightly more connective tissue than normal but parenchyma may be considered normal. At one place in the cortex there are some structures of deep layer included in vesicular layer. This seems like a structural malformation.

NECROSES.

Focal necroses of the spleen affecting chiefly follicular centres but also chords, are not at all uncommon in avian spleens, especially where parasitism occurs, not only with hemic protozoa and embryos, but also with intestinal or visceral nematodes and trematodes.

SPLEEN IN ANEMIA.

The spleen in the anemias shows much less definite change than one would expect. In the secondary form of anemia among mammals one finds a slight excess of pigmentation and an occasional fibrosis but often the size of the organ is recorded as normal. When the impoverished blood seems secondary to skeletal degenerations there is a diffuse or follicular enlargement. In the birds, on the other hand, there is nearly always some grade of enlargement which is due in the well studied examples to a richness of blood cells. There may be a slight increase in follicles, but these bodies are usually small and solid. In two instances a prominence of large endothelial cells was discovered. Pigment is seldom increased, but it may be very excessive.

In the primary anemias little more than the above is to be found. Fibrosis is more evident and perhaps pigmentation less so, but the variations are more of degree than kind. The spleen in leucemia can only be discussed upon the case already reported (_q. v._).

SPLEEN IN HEPATIC FIBROSES.

The fibroses of the liver are not infrequently associated with some enlargement of the organ under discussion. At this laboratory hepatic cirrhoses are divided into Portal, Biliary, Fatty, Perilobular and Vascular. By a study of the spleens in these cases a few facts have been obtained. In mammalian portal cirrhoses there is usually a very moderate but definite increase in the size of the spleen due to connective tissue increase in the trabeculæ and reticulum, with very small compact follicles. Among the birds the organ seldom shows more that a moderate congestion and diffuse hyperplasia. In the mammalian biliary cirrhoses there is almost without exception a definite enlargement due to fibrosis and follicular hyperplasia. Among the birds the process is very far from uniform, there being just as often no change, as a congestion and hyperplasia, or as a mild fibrosis; it is notable, however, that pigmentation is commonly met in this class. No noteworthy change is met with in the spleen of fatty hepatic cirrhoses. We have no record of cyanotic induration of the spleen accompanying a similar condition in the liver. When the condition of perilobular hepatic fibrosis has been met a distinct increase of the splenic pigment is usually found. In reviewing the facts in this paragraph one is forced to the conclusion that, with the exception of the frank infective cases, there is no definite relation of the splenic changes to those in hepatic cirrhosis, a fact made perhaps the more significant in view of the idea held in some quarters that the primary change in this pathological process occurs in the spleen.

PERISPLENITIS.

Perisplenitis of an acute or fibrosing variety as a part of peritonitis or as the result of an injury to the splenic region, has been encountered on numerous occasions and offers nothing worthy of comment, but the so-called “sugar-icing” spleen, associated with perihepatitis and general peritoneal thickening, and with an obscure relation to tuberculosis has not been seen. As we shall learn later peritoneal or massive intestinal tuberculosis is not common in the lower animals. A diffuse fibrous thickening of a pearl gray glistening appearance, has occurred in five monkeys harboring the Filaria gracilis in the peritoneum.

TUBERCULOSIS.

In tuberculosis of this organ the capsule is almost invariably thickened over the nodules, but not over the whole organ and rarely in the diffuse variety. There is almost always, however, in this prolonged infectious disease some reaction on the part of the spleen, particularly when several other viscera are involved. In such cases a low grade of general hyperplasia and fibrous tissue increase is found. This is especially true in the Primates and Carnivora in long continued pulmonary tuberculosis, and it is in this form that one does not often see tuberculous lesions proper in the spleen itself. Tuberculosis of the spleen is not very common in adult human beings and domesticated animals, while in the young it is seen in a fairly high percentage of cases. In the wild animals this organ seems much more susceptible to the settling of tubercle bacilli as will be attested by the facts to be cited, and yet there are some conspicuous exceptions to this statement. Just why certain groups, or orders should show splenic tuberculosis very frequently while others fail to do so is far from clear.

The appearance of the lesion is fairly comparable throughout the animal kingdom, variations among the Aves being chiefly in the more frequent occurrence of the diffuse tuberculous splenitis. Miliary, caseous and conglomerate masses occur separately or together and without very distinct relation to other pathological involvements.

The relative incidence of tuberculosis in the spleen is set forth in the section devoted to this infection, but may be mentioned here in a general way. The organ is about equally susceptible to the disease in mammals and birds according to the figures, but the high percentage for the former is due to the frequency with which tuberculosis is met in the Primates. With this order deducted there is no doubt that the avian spleen has a greater vulnerability for the tubercle bacillus than has the mammalian organ. Rodentia as a mammalian order stand next to the Primates, whereas the Carnivora and Ungulata relatively seldom show splenic tuberculosis. Among the Aves one finds that Columbæ, Galli and Accipitres have the highest splenic susceptibility, but beyond this one hardly dare venture because of the irregularity in the number of specimens seen at autopsy. Suffice it to say that a greater number of cases of tuberculosis are seen in the spleen of the class for which the intestinal origin of tuberculosis appears most important.

In the cases of actinomycosis and its congeners, such as the Kangaroo maxillary mycosis, which we have seen at the Garden, no specific changes have been seen in the spleen, unless a single or double nodule of the same variety as the original focus may be considered specific. Such was found in two cases, one a tapir with low grade inactive actinomycosis, the other a kangaroo with maxillary streptothricosis. Two deer came to autopsy with a gross picture suggestive of anthrax; no bacilli could be found in the semifluid spleen, but a member of the hemorrhagic septicemia group was found. The latter group of infections has been fairly well represented, although not in epizoötic form, and the almost invariable splenic change has been that already discussed as diffuse splenitis. Three secondary tumors are recorded, two cancers and one renal adenoma.

SECTION VI THE RESPIRATORY SYSTEM AND ITS RELATED STRUCTURES