Part 8

Marsupialia present three quite interesting cases, a Tasmanian Devil (_Sarcophilus ursinus_) and two Kangaroos (_Macropus_). The first showed distinct sacculations in the ascending aorta, suggestive of Mönckeberg’s sclerosis but equally resembling several small or incomplete aneurysms. The underlying vessel was opaque and stiff, continuing so to the middle of the thoracic portion. The other marsupials showed distinct mesial damage with early calcification and a roughened intima; once the pulmonary artery was involved.

It will be noticed that the orders Rodentia and Lemures are missing from those showing arterial disease although we have a reasonable number of autopsies upon them.

Passeres are hardly good exponents of vascular disease, an interesting thing in view of their large heart, heavy vessels, and flying habits. It is, however, striking that two of the three birds of this group had aneurysms of the aorta, one of which ruptured just above the origin, partly into and partly outside the pericardium. Despite several microscopical sections we were unable to find the tiny ends of the breach and any evidence of parasites. In the other case a vegetative growth occurred on the intima near the dilatation.

The Picariæ were represented by a Hornbill and a Toucan. The former presented roughened yellowish elevations for two centimetres above the aortic valve; this seemed the only involvement. The Toucan had a few small scattered but deep yellow plaques in the same location.

Psittaci, although failing to be accredited with a high percentage of arterial disease, nevertheless present some striking and interesting changes. In the first place, the central vessels are not so conspicuously the principal seat of atheroma as is the case in many other orders, and the lesions are not so productive. It is usual to find flat areas of opacity, perceptible as easily by section through the wall as by holding up the opened vessel to the light, the seat of the density being in the media. This can be followed into the wing arteries and, upon microscopic section, these smaller vessels will show mesial degeneration, thus being comparable to arteriocapillary fibrosis of man. However frequent this picture may be, there are also instances of overgrowth in the intima, prominences over opacities or raised plaques at the points of branching, lesions which correspond to the activity of the inner coat. It is interesting that renal disease, chronic pulmonary and general infections occur in a goodly proportion of these birds.

Striges is an order of little importance. The lesions in the two cases consisted of rather prominent plaques in aorta and large branches.

Accipitres stand out as giving the greatest percentage of any order of which we have had a fair number upon which to make comparisons. Their arterial lesions are frequently accompanied by renal, myocardial and valvular disease. Mesial and intimal alterations are about equal in degree, irregular patches going on to softening without ulceration, and early calcification being quite prominent. The sickle at the branching of the renals is a favorite site of deposit. Like the parrots their arterial damage is not confined to the aorta, but may be found in the carotids, femorals or small wing arteries. The most common situation is, however, in the lower thoracic and renal regions.

Galli, represented by five specimens, seem to have their vascular disease accompanied very often by myocardial and infectious disease. Their arterial pathology consists of raised gray patches in the aorta only.

Steganopodes give the highest percentage among avian orders, but this must be held _sub judice_ because of the small number of specimens subjected to autopsy. Renal disease occurred in three cases. Their lesions are in the form of yellow opaque streakings in the aorta and its branches, in one case following the carotid half way up the neck. Plaques are not common, and when they occur are streaky and illy outlined.

Herodiones, represented only by a heron, are negligible. This bird showed a diffuse thickening with early thrombotic deposits attached to the intima.

Palamedes are represented by a Screamer which showed around the orifices of the renal arteries an early fatty deposit and mesial opacity.

Anseres present a considerable number of cases which are accompanied by cardiac, renal and general pathology. The character of the lesions is like that of the Accipitres and the distribution differs in only one particular. In four of these eleven cases the elevations or opaque areas were limited entirely to the stretch of aorta which might be compared to the arch in mammalia, that is the part with which the right subclavian is in closest contact and which bends almost directly backward to become the thoracic aorta. This excludes the ampulla just above the aortic valves. There seems no real reason for this and it may be accidental.

Struthiones, with seven specimens having arterial disease in the great vessels alone, seem to have no especial characters unless these be in the heavy furrowing and stiffness of the wall, with opaque, elevated, indefinite patches, seen mostly in the descending aorta; once a long tough and partly brittle stretch was found in the carotid.

Alectorides, with a relatively high percentage, present irregularly outlined fatty and finely granular patches in the intima of the lower aorta and abdominal vessels, and, in two cases, as far as the vessels of the lower extremities could be followed.

The orders Columbæ and Fulicariæ are missing from the list of Aves having arterial disease, yet a reasonable number of autopsy records are at hand.

SUMMARY ON ARTERIOSCLEROSIS.

Having discussed the orders separately, a review of the whole situation is desirable. Chronic arteritis, or as it is usually called arteriosclerosis, is common to very many zoological orders, and its principal lesions are comparable throughout the two classes under consideration. A statement as to its incidence would best be made by adopting an arbitrary number of observations as the desired minimum upon which to draw conclusions, and I shall adopt one hundred as such a figure. Accepting this as reasonable, a review of the table indicates that the order of percentage incidence is: Accipitres 6.6, Ungulata 3.5, Anseres 3.4, Carnivora 3.3, Striges 2.2, Psittaci 1.8, Marsupialia 1.8, Galli 1.6, Primates 0.6, Passeres 0.22; the other orders have less than one hundred specimens each. There is no doubt that carnivorous birds have the highest incidence of chronic arterial disease. Next in order come three varieties with nearly equal incidence, the ungulates, anserine birds and carnivorous mammals. These orders have little in common unless it be that in nature they are often engaged in prolonged or strenuous effort, as in fight or flight. We possess no measurement of their vascular supply but by consultation of the table giving heart weights (page 63) it will be found that three of them have values below that of the class in which they belong; the Carnivora alone have a greater heart-to-body ratio than the average for its class Mammalia. Nor do these orders have any direct dietetic relationship. The expected longevity of these groups does not permit one to discover any reason for arterial changes except perhaps that they have a reasonably good viability under park conditions, and therefore many have a longer opportunity to develop vascular disease. It so happens, however, that the first four groups are the most likely to suffer from gastrointestinal inflammation, of dietetic or bacterial origin.

It is interesting, but not easily explicable that the orders of great activity, Primates and Passeres, are at the end of the list; their food is very largely carbohydrate in character. Just why Lemures, Rodentia and Columbæ should be missing is not quite clear, because orders of comparative habits and food are included.

A review of the concomitant pathology reveals the fact that nephritis more often accompanies these processes than any other single condition. Among the chronic infectious disease in the table is included chronic enteritis; this group falls well behind the renal diseases. The relatively small number of cases of valvulitis speaks rather against an active infectious origin of the vascular lesions.

ANEURYSMS.

Aneurysms have been observed all over the world and in nearly all the larger orders. The London Garden has had an unusually large number to report, the most striking being that described by Seligman in the 1906 Report of the Society, in a tiger thirteen years in captivity which had fourteen sacculations from pea to plum size scattered along the aorta. Even with the number of cases on record and those collected here it would be unwise to draw deductions as to their incidence or as to the possibilities of vascular dilatation in any given order. Horses have aneurysms occasionally, cows and dogs rarely, according to Rievel. I can, however, state that there has not occurred in our experience a large growing pulsating aneurysm in the aortic arch region comparable to the condition so well known in man. The literature to which we have had access gives a definite impression that parasitism of vessel walls is the most important factor in the causation of ectasia, and that simple non-parasitic arteriosclerosis is relatively unimportant. Two of our seven cases seem to have been free of parasites but the notes cannot entirely assure one of this. The distribution of cases at this Garden is found in Table 5.

A dilatation of the first part of the arch in a seal to a size which might be described as an aneurysm caused us to make such a diagnosis, correctly enough from the size and shape of the vessel but possibly worthy of reconsideration in light of the fact that no damage to the wall was found. At the heart and in the descending arch the diameter measured 4–5 cm., while the first part of the aorta measured 7.5 cm. This great irregularity in width could not be found in other seals albeit this section of the arch is usually a trifle larger than its origin and descending portion. The cava in seals is also large, but in this particular animal it measured 6 cm. across at the liver where there is a normal dilatation. These two spaces are looked upon as normal reservoirs for blood during diving, but the case in question seemed to have excessive “aneurysmoid” enlargements without mural disease. London reports an aneurysm of the aorta in a seal.[17]

Aneurysms are not so common in birds, the incidence being in comparison with mammals as 1 to 2.2. Two seats are prominent for their development: the sinuses above the aortic valves and the first part of the subclavian vessels; two of the six cases occupied the first position, two the second, while one other lay in the arch of the aorta, the last in its descending thoracic portion. Those developing over the valves seem to arise from simple degenerative arteritis; those that occupy the other locations are apt to be surrounded by plaques on the intima. Aneurysms in birds reveal by microscopy some trace of all the vascular coats and seem not to construct an adventitia from surrounding areolar tissue. The veins have presented no peculiar pathology, except in tumors which will be taken up later. A Derby’s Tyran showed a phlebitis and periphlebitis of the left subclavian vein, of mycotic nature, which led to death by rupture and hemorrhage.

SECTION IV DISEASES OF THE BLOOD AND BONE MARROW

The production and physiology of the circulating blood seem closely similar in the two classes under consideration, although the anatomy is not the same in birds and mammals, variations also occurring within the latter group. Pathological responses follow comparable lines in that hemolyzing agencies, be they hemosporidia, absorptions from metazoan parasites or bacterial toxins, produce a reaction in erythropoietic centres, and positively chemotactic viruses call forth increases in the colorless elements. We have also observed a decrease of leucocytes in an Orang Utan suffering from influenza, a finding analogous to that in the human attack. There is, however, a much less ready response on the part of birds to any leucocyte-stimulating influence, in this class the mononuclears seeming to bear much of the burden assumed by the myeloid cells of Mammalia or at least appearing on the stage very quickly so that any increase of the latter is overshadowed by them. Perhaps this apparent difference may be further explained by the greater number of colorless blood cells, structures which might be called the principal secondary defences of the body and constantly at the disposal of the organism, normally present in the birds’ blood; they amount to 25,000 per cubic millimetre in birds, while in the mammals very few varieties have half this number. On the accompanying Table (6) will be found a few differential leucocyte counts now known to us.