Part 7

The differences between classes are not so conspicuous between orders. However, the large heart of the carnivores increases both its muscle and chambers, while the small heart of the rodents and marsupials more often dilates. Analysis of the avian orders is inconclusive and somewhat contradictory. Let it suffice to say that the birds which fly most, with exception of the ducks, have a relatively low vulnerability, and the soaring carnivorous Accipitres and the largest birds, Struthiones, apparently have a high susceptibility to damaging influences and enlarge their muscle bulk in response to increased work.

Aneurysms of the heart are quite rare; only two have been seen. They were both located at the apex of the left ventricle in birds; they did not rupture. Myocardial damage is evident in both cases but the cause is not clear; parasites could not be demonstrated. Plimmer reports a case of cardiac aneurysm at the apex from infestation of the heart muscle by sarcosporidia.

SECTION III DISEASES OF THE BLOOD VESSELS

The gross anatomy of the blood vascular system is constructed upon the same general scheme throughout mammals and upon a comparable basis in birds. Microscopically there is little variation throughout the orders unless it be in the relative proportion of muscular and connective tissues. The origin of the great vessels at their cardiac base and their distribution to the pulmonary and to the greater circulations in no way differ in these two classes in that it always consists of an efferent pathway to the lung and a root vessel above the aortic orifice. The former has usually quite a distinct origin on the right side, but in some birds the posterior wall of the pulmonary artery may overlie the entire aortic base; this, however, is not the rule for birds. The aorta in most mammals remains a separate and distinct vessel for some distance, after which it gives off the innominate and subclavians. In the birds on the other hand, the stretch immediately above the aortic valve is usually ballooned out somewhat, into a sort of sac or ampulla from which the subclavians and descending aorta arise. This forms a structure of rather trident shape, the lateral prongs being the subclavians, the middle and posterior being the aorta proper. In some birds the aorta may have the length of a centimetre or more then dividing into the left subclavian and right aorta from which the right subclavian comes off.

There is definitely more support to the heart and vascular roots in mammals than in birds, in the latter class these structures lying quite free between the lateral air sacs and well in front of the lungs. Nor is there the richness of mediastinal areolar and fatty tissue in the winged creatures.

The vessels of mammalia retain a considerable wall throughout nearly their entire length. At first the wall is thin compared to the calibre of the vessel while the arteries smaller in calibre, have a heavy wall. In birds the arterial stalk at the heart is supplied with very heavy walls, but after the second branching the relation of wall to calibre seems to continue about the same. In this class the stalk vessels have wall to calibre relation of 1 to 3 (measurements in 2 Passeres, 1 Psittaci, 1 Accipitres) whereas in mammals the relation varies from 1 to 5 to 1 to 7 (observations on 2 carnivores, 1 ungulate, 2 rodents). In mammals the consistency of a normal artery wall remains much the same, a firm, resilient, yellow-white tissue, quite opaque and standing open upon cross section. In birds this description covers the main stalk, the aorta in the abdomen and the first part of the carotid and iliacs. When these characters are lost, the arteries become semitranslucent bluish strands so that they are difficult to follow in the muscles of the neck and extremities. This is particularly true in the Passeres, Picariæ, Galli and Columbæ while in the Psittaci, Accipitres, and Anseres the arteries are distinctly whiter than the veins but yet quite soft. In the Herodiones and Struthiones, thick walled vessels may be followed as far as the second joint in both extremities. These differences depend in part upon the grosser construction of the central arteries in Aves and in part upon the larger amount of elastic tissue in them than in the secondaries and smaller vessels, and than in comparable mammalian vessels.

It is impracticable to go into the minutiæ of histology in the different orders, which indeed varies but little, although attention might be directed to the facts that in all central vessels the relative amount of elastica is greater than in smaller ones and that muscular tissue seems to exceed in the latter. Considerable work has been done upon the amount and arrangement of muscle bands in isolated genera, but no comprehensive data are at hand upon orders. The strands of muscle do not seem arranged so regularly as in mammals; the pulmonary artery of the cat, for example, has a muscle arranged like an oblique band in waves or festoons along the length. The mammals as a class seem more richly supplied with arteries and veins than do the birds, and the square area of the vascular system is likewise larger. This is distinctly different from the amount of heart bulk as given in the discussion of kilogram-heart ratios so that one might say that the birds are “overhearted and undervesseled.”

In so far as the physiology of the two classes is concerned it is obvious that a different regulatory system is necessary because, aside from the variations of pressure incidental to pulmonary, muscular and visceral work, there remains the altering pressure within the air sacs of Aves, a force different under states of rest, of running, of deep water swimming and of flying with or against the wind. Part of the internal air pressure variation is cared for by the ability a bird has to respire the air in its sacs and bones, but in prolonged exposure to the pressure under water or during protracted flight some compensatory mechanism doubtless exists. This seems to reside in part in the heavy elastic quality of the arterial stalk and the very rich venous supply of the abdomen, including the renal-portal system and the distensible pelvic veins. Just where the governing power for this mechanism resides is as much a matter of debate as in the case of the human being, but certain researches would place it in the caudate lobe and pituitary body.

Having discussed these general comparative data we can now pass to a consideration of the pathology seen at this Garden. The subject will be studied from the standpoint of the vessels as a system and the changes peculiar to it. Naturally the most important lesions affect the great stalks and the principal trunks, from which the processes may continue into the smaller vessels. The essential alterations are inflammatory and degenerative, of which the latter are by all odds the more important. The former are either involvements of the vessel walls by frankly infectious processes, or less easily proved to be bacterial in origin, as is the case with periarteritis nodosa. Acute arteritis and phlebitis are constantly encountered and present nothing unusual. General nodal periarteritis has been seen in the lower animals, Lupke having reported[14] before the German Pathological Society a big outbreak in cows, but it is less common than among men; we have not discovered it here.

THROMBOSES.

Thrombosis is practically always a parasitic or an infectious process although at times considerable difficulty is encountered in explaining the source of the worms or bacteria. Thus, for example, the iliac or femoral thromboses which are at the bottom of intermittent claudication, are frequently quite vague in origin. We have had one such case in a deer in which a partly occluding thrombangeitis existed in both femoral arteries and veins. Mesenteric thrombosis, a serious condition in cattle and horses from infestation with sclerostomum or strongylus, has not been proven at the Garden, but we have seen one case of numerous thromboses of the venous radicals in the jejunal wall apparently due to some nematode larvæ; the specimens were so soft by decomposition that determination was not attempted. There occurred a thrombosis of the cava and aorta originating from a necrotizing cloacitis, apparently streptococcal in nature, in a Demoiselle crane. The clot, while not totally occlusive, extended nearly as far as the heart in the vein and the abdominal aorta. There is also on record a thrombosis of the vena cava and right pulmonary vein in an American beaver, harboring Hepaticola hepatica in the liver, with a fibrosing pneumonia due to this parasite. Another case in which parasites seemed to take a hand concerned a common raccoon with tapeworms (sp.?) in the small intestine and microscopically discoverable parasitic parts in the lungs; these organs were the seat of extensive congestion and venous thrombosis, the latter containing really enormous numbers of diplococci. The parasites probably paved the way for bacterial invasion. A frank case of septic thrombotic aortitis was noted in a Rice Grackle, the infectious focus apparently being a vegetative “tricuspid” valvulitis.

ARTERITIS.

In addition to these cases, productive inflammatory changes were discovered five times affecting vessels in or near frank inflammatory processes. The animals affected with this productive process were three birds, a rodent and an elephant. In the case of two birds and the rodent the process was associated with chronic intestinal lesions, while in the elephant it was found as an endarteritis obliterans in large vessels of the lung of chronic pulmonary tuberculosis occurring in this animal. These instances serve as examples of the truly productive inflammatory processes affecting vessels and illustrate the distribution through the animal kingdom. Pathogenetically there are no essential differences, and histologically they correspond to the forms seen in man. Had every piece of tissue been subjected to microscopy wherein such lesions might have existed, more examples might have been discovered, but these processes excite no peculiar secondary effects so that attention is not drawn to them directly. The only noteworthy difference between mammals and birds is the fragile character of the clots in the latter class. This is peculiar because the principal response of this class to an infectious irritant is coagulation necrosis, liquefying enzymes apparently being absent or small in quantity.

Fatty deposits in the aortic intima are by no means uncommon in the human subject and are encountered at all ages, even in youth at a time when progressive arteriosclerosis does not accompany them. There is a belief in many quarters that this fat may be laid down and then removed. Such deposits are exceedingly rare in wild animals; when they occur it is in small indefinite patches and not the bands or rows as found in man.

TABLE 5.

_Table Showing the Incidence of Degenerative Arterial Disease, the Percentage in Animals Subjected to Autopsy and the Principal Associated Pathology._

════════════════╤═════╤══════════╤═════════╤═════════╤══════════ │Total│Percentage│ Due to │Aneurysms│Myocardial │ │ of order │parasites│ │ disease │ │ │ │ │ ────────────────┼─────┼──────────┼─────────┼─────────┼────────── Primates[15] │ 3│ .6│ │ │ 3 Carnivora │ 16│ 3.3│ 5│ 7│ 1 Ungulata │ 13│ 3.5│ 2│ │ 1 Marsupialia │ 3│ 1.8│ │ │ Total │ 35│ 1.8│ 7│ 7│ 5 │ │ │ │ │ Passeres │ 3│ .22│ │ 2│ Picariæ │ _2_│ 2.2│ │ │ Psittaci │ 13│ 1.8│ │ 1│ Striges │ 3│ 2.2│ │ │ 1 Accipitres │ 13│ 6.6│ │ 1│ 4 Galli[16] │ 5│ 1.6│ 1│ │ 4 Steganopodes[16]│ _5_│ _25._│ │ │ Herodiones │ 1│ 1.│ │ │ Palamedes │ _1_│ _20._│ │ │ 1 Anseres │ 11│ 3.4│ │ 2│ 4 Struthiones │ _7_│ _22._│ │ │ Alectorides │ _2_│ _5.4_│ │ │ 1 Total │ 66│ 1.8│ 1│ 6│ 15 ────────────────┼─────┼──────────┼─────────┼─────────┼────────── Grand Total │ 101│ 1.8│ 8│ 13│ 20 ────────────────┴─────┴──────────┴─────────┴─────────┴──────────

════════════════╤══════════╤═══════╤═════════╤══════════ │Valvulitis│ Renal │ Chronic │ Chronic │ │disease│pulmonary│infectious │ │ │ disease │ disease ────────────────┼──────────┼───────┼─────────┼────────── Primates[15] │ │ │ │ 1 Carnivora │ │ │ 1│ 5 Ungulata │ 1│ 2│ 3│ 2 Marsupialia │ │ │ │ Total │ 1│ 2│ 4│ 8 │ │ │ │ Passeres │ │ │ │ Picariæ │ │ │ │ Psittaci │ │ 6│ 3│ 2 Striges │ 2│ │ │ Accipitres │ 2│ 5│ 2│ 4 Galli[16] │ │ 2│ 1│ 2 Steganopodes[16]│ 1│ 3│ │ Herodiones │ │ │ │ Palamedes │ │ 1│ │ Anseres │ 1│ 4│ 1│ Struthiones │ │ 1│ 2│ 3 Alectorides │ │ 1│ │ Total │ 4│ 25│ 9│ 11 ────────────────┼──────────┼───────┼─────────┼────────── Grand Total │ 5│ 27│ 13│ 19 ────────────────┴──────────┴───────┴─────────┴────────── For meaning of italics see foot note Table 1.

DEGENERATIVE ARTERITIS OR ARTERIOSCLEROSIS.

Whether or not it be exact to speak of the more protracted forms of vascular disease usually called arteriosclerosis or atheroma as degenerative, such changes form the most pronounced features of the lesions, and we have made such a separation at this laboratory. Here is not the place to engage in the academic discussion of the nature of the process, but I wish to state that collectively the changes as seen in such lesions in the lower animals are more degenerative than productive, and that we have never seen true ulcerative atheroma as it not uncommonly appears at the autopsy table in any large hospital. This disease of the vascular walls has long been attributed to alcohol, gout, syphilis and other such prolonged intoxications to which we might apply the light term of “toxins of civilizations.” Too little credit, or discredit has been given to chronic intestinal disorders, overeating, and overdrinking of ordinary fluids, to entirely incorrect diets, and to chronic bacterial diseases. Even though the exact counterpart of the disease in man does not occur in lower animals, we shall see the probable association with food and with habits, in a manner discordant with former teaching of the causation of the disease.

The group to which the name degenerative arteritis has been applied is, as has already been indicated, more productive than the analogues seen in the human being, but indeed it is questionable whether the lesions even in the lower animals are not more degenerative than productive. Since, however, chronic arteritis is always associated with damage to the elastic and muscular fibres of the media as well as with fatty change and overgrowth of the intima, all the deforming and degenerative cases will be classed together.

The general picture in mammals is one of diffuse rather than of plaque- like thickening, but well outlined raised or depressed areas are encountered. In the aorta and larger branches one may find irregular streaking and loss of elasticity with fairly clear, pale yellow or gray, flat sections of distinct opacity. Rarely these may contain calcareous matter, a change most often seen in the carnivores. The lesions are very largely limited to the aorta; 26 or 76 per cent. of the 35 cases had this distribution alone. The arch seemed never to be affected alone, and indeed it is rather commoner to find opaque patches stretching along the thoracic or even abdominal portion; this is especially true of the Ungulata.

There have been also in mammals five cases of mesial change which have given rise to the picture described by Mönckeberg and usually entitled by his name. However, the noteworthy differences between the wild animal and the human cases are the absence of advanced calcification in the media under the concavities and the prominence of the changes in the aorta near the heart to be found in the former. These few cases do not permit an association of the arterial disease with any particular pathology in other parts.

Considered minutely, the outstanding lesion in the class Mammalia is the separation of the elastic fibres by fluid and debris, apparently derived from the degenerated muscle fibres, associated with a decrease of round and elliptical nuclei. Globules and hyaline pink staining material are often collected between split-up elastic strands, which fibres in some cases seem quite numerous, in others reduced. In the intima heaping-up of cells and fibres is very moderate in degree while usually one finds only subendothelial edema. When the process has advanced far, the microscopy is like that of well developed human lesions. Arterial degeneration due to parasites gives a different picture in that medial degeneration is far advanced and some fibrinocellular activity is seen upon the intima when this tissue remains. When, however, the infestation has proceeded to weaken the wall sufficient for it to give way into an aneurysm, little or no vestige of the true arterial wall is left.

In the Aves the distribution and anatomy of this process present some differences. The aorta is as usual most conspicuously the seat of change, but it is noteworthy that the dilatation or ampulla immediately above the aortic valves and from which the main vessels spring, is practically always free of lesions which are on the other hand most marked in the thoracic and abdominal sections. One’s attention is usually attracted to the aortic surface by its roughness although visibly there may be no plaques, but upon close inspection a mottled opacity may be detected. This all seems due in the few cases subjected to tissue section, to hyperplasia of endothelia, with or without fibre increase. The media may show muscular granularity or no change at all. At the stage when plaques are formed, fairly well outlined, firm but rather brittle, raised areas are detected, seated upon a distinctly opaque gray wall. The remainder of the vessel may be smooth and elastic but sometimes, in the Accipitres for instance, a general resistance to pressure and tension is found. Microscopically such a vessel will show a media the seat of ruptured muscle fibres, split-up or broken elastica and some debris, while the intima is covered with active and distinct fibrocellular exudate.

I have for comparison divided the cases into those in which the superficial productive character was prominent and those seemingly entirely a degeneration of the media, that is with inactive intima. In mammals 77 per cent. of the cases were of the degenerative type while in birds 50 per cent. were of this kind. The exact importance of this difference is not easy to evaluate, but with the facts that the bird has a greater elastic supply for its large vessels and a greater wall to calibre ratio, it is interesting. The aorta alone was affected in half of the birds, the remainder showing lesions in the carotids and femorals.

The tendency for the media to degenerate would lay the basis for concavities on the intimal surfaces after the type seen in Mönckeberg’s sclerosis. A number of cases of this variety have been encountered, but instead of being better developed in the vessels of extremities as in man they have presented more definite pictures in the aorta and pulmonary vessels. Examples will be quoted under the discussion of the various orders.

Primates are not often affected with degenerative arterial disease, two of the instances observed showing this change confined to the coronary vessels. As might be expected the myocardium in both was affected, and in one animal had a definite concentric hypertrophy. A very interesting case was encountered in a Lion-tailed Macaque (_Macacus silensis_). His heart showed distinct fibrosis of the conducting pathways from auricle to ventricle and of the papillary muscles. No atheroma was present in the aorta, but in the pulmonary distinct sacculations of the Mönckeberg type were found. Mesial degeneration was apparently responsible, but no calcification had occurred. Death was due to acute gastritis.

Carnivora present about half the cases seen in mammals and 16 per cent. of the total. Five of the sixteen cases owe their origin to parasitic arteritis and were combined with aneurysms. As will be noted by consultation of the list there is no outstanding accompanying pathology, a fact which makes parasites more important. One case of mesial degeneration, resembling the Mönckeberg type was observed in the thoracic aorta of a bear.

Ungulata are generously represented, thirteen cases being recorded distributed rather unevenly between the odd-toed (1 or 8.5 per cent.) and even-toed groups (12 or 2.9 per cent.). The single case in the first group occurred in a Zebra (_Equus burchelli_) wherein was found about the middle of the thoracic aorta a diffuse thickening of media and intima in a circular plaque approximately two centimetres in diameter; it was by no means so well developed as similar lesions in the even-toed ungulates. This recalls the expression of doubt by Zinserling as to the occurrence in the horse of arteriosclerosis similar to that in human beings.

The lesions in the Artiodactyla are both in plaques and diffuse, the aorta and its branches sometimes being quite wrinkled but beset with firm elevations with and without calcification. These changes are fairly definite and, although they never attain the development seen in man, resemble the stage of wrinkling and roughness in the preulcerative stage of the human analogue. Two of the cases were associated with dilatations of the mesenteric vessels and with periarteritis, a picture strongly suggesting parasitic infestation; in one case ineffectual search was made, in the other no record is made of the parasites. Renal disease occurred only twice and myocardial damage only once. Chronic pulmonary disease, present thrice, took the form of tuberculosis twice and pleural adhesions with atelectasis once.