Part 6

═════════════╤════════════════════════════════════════════════════════ Heart of │ Hypertrophy ─────────────┼─────────┬───────┬─────────┬─────────┬───────┬────────── „ │Pulmonary│ Renal │ Chronic │ Acute │Thyroid│Myocardial │ Disease │Disease│Infection│Infection│Disease│ Disease │ │ │ │ │ │ │ │ │ │ │ │ ─────────────┼─────────┼───────┼─────────┼─────────┼───────┼────────── Primates │ 3│ 1│ 1│ 1│ │ Lemures │ │ │ │ │ │ Carnivora │ │ 2│ 6│ 1│ 3│ 4 Pinnipedia │ │ │ │ │ │ Rodentia │ │ │ │ │ │ Insectivora │ │ │ │ │ │ Chiroptera │ │ │ │ │ │ Proboscidea │ │ │ │ │ │ Hyracoidea │ │ │ │ │ │ Ungulata │ │ 4│ │ │ │ 2 Edentata │ │ │ │ │ │ Marsupialia │ │ 1│ │ │ │ 1 Monotremata │ │ │ │ │ │ Total Mammals│ 3│ 8│ 7│ 2│ 3│ 7 │ │ │ │ │ │ Passeres │ │ │ │ │ │ Picariæ │ │ 1│ │ │ │ Striges │ │ │ │ │ │ Psittaci │ │ │ │ │ │ Accipitres │ │ 3│ 1│ 1│ │ 5 Columbæ │ │ │ │ │ │ Pterocletes │ │ │ │ │ │ Galli │ │ 1│ │ 1│ │ 1 Hemipodii │ │ │ │ │ │ Fulicariæ │ │ │ │ │ │ Limicolæ │ │ │ │ │ │ Gaviæ │ │ │ │ │ │ Pygopodes │ │ │ │ │ │ Impennes │ │ │ │ │ │ Steganopodes │ │ │ │ │ │ Tubinares │ │ │ │ │ │ Herodiones │ │ │ │ │ │ Odonotoglossæ│ │ │ │ │ │ Palamedes │ │ │ │ │ │ Anseres │ │ │ 1│ 1│ │ 1 Struthiones │ │ │ 1│ 1│ │ 1 Crypturi │ │ │ │ │ │ Total Birds │ 0│ 5│ 3│ 4│ 0│ 8 ─────────────┼─────────┼───────┼─────────┼─────────┼───────┼────────── Total │ 3│ 13│ 10│ 6│ 3│ 15 ─────────────┴─────────┴───────┴─────────┴─────────┴───────┴──────────

═════════════╤═════╤═══════════════════════════════════════════ Heart of │ │ Dilatation ─────────────┼─────┼────────┬────────┬────────────────┬──────── „ │Total│Percent.│Valvular│Arteriosclerosis│Diseases │ │ for │Disease │ │ of │ │ Order │ │ │Thoracic │ │ │ │ │ Serosæ ─────────────┼─────┼────────┼────────┼────────────────┼──────── Primates │ 4│ .8│ │ 1│ Lemures │ │ │ │ │ Carnivora │ 11│ 2.2│ │ 1│ 2 Pinnipedia │ │ │ │ │ Rodentia │ 8│ 4.2│ │ │ Insectivora │ │ │ │ │ Chiroptera │ │ │ │ │ Proboscidea │ │ │ │ │ Hyracoidea │ │ │ │ │ Ungulata │ 11│ 3.│ │ │ 4 Edentata │ 2│ _12.5_│ │ │ Marsupialia │ 8│ 4.5│ │ │ Monotremata │ │ │ │ │ Total Mammals│ 44│ │ 0│ 2│ 7 │ │ │ │ │ Passeres │ 1│ │ │ │ Picariæ │ │ │ │ │ Striges │ │ │ │ │ Psittaci │ 1│ .1│ │ │ Accipitres │ 1│ .5│ │ │ 1 Columbæ │ │ │ │ │ Pterocletes │ │ │ │ │ Galli │ 2│ .7│ │ 1│ 1 Hemipodii │ │ │ │ │ Fulicariæ │ │ │ │ │ Limicolæ │ │ │ │ │ Gaviæ │ │ │ │ │ Pygopodes │ │ │ │ │ Impennes │ │ │ │ │ Steganopodes │ │ │ │ │ Tubinares │ │ │ │ │ Herodiones │ │ │ │ │ Odonotoglossæ│ │ │ │ │ Palamedes │ │ │ │ │ Anseres │ 5│ 1.5│ │ │ 1 Struthiones │ │ │ │ │ Crypturi │ │ │ │ │ Total Birds │ 10│ │ 0│ 1│ 3 ─────────────┼─────┼────────┼────────┼────────────────┼──────── Total │ 54│ │ 0│ 3│ 10 ─────────────┴─────┴────────┴────────┴────────────────┴────────

═════════════╤════════════════════════════════════════════════════════ Heart of │ Dilatation ─────────────┼─────────┬───────┬─────────┬─────────┬───────┬────────── „ │Pulmonary│ Renal │ Chronic │ Acute │Thyroid│Myocardial │ Disease │Disease│Infection│Infection│Disease│ Disease │ │ │ │ │ │ │ │ │ │ │ │ ─────────────┼─────────┼───────┼─────────┼─────────┼───────┼────────── Primates │ 1│ │ │ 1│ │ 1 Lemures │ │ │ │ │ │ Carnivora │ 2│ 4│ 1│ 2│ 3│ 2 Pinnipedia │ │ │ │ │ │ Rodentia │ 3│ 2│ 2│ 4│ │ Insectivora │ │ │ │ │ │ Chiroptera │ │ │ │ │ │ Proboscidea │ │ │ │ │ │ Hyracoidea │ │ │ │ │ │ Ungulata │ 1│ 2│ 2│ 2│ │ 1 Edentata │ 1│ │ 1│ │ │ 1 Marsupialia │ 1│ 3│ 2│ 2│ │ 1 Monotremata │ │ │ │ │ │ Total Mammals│ 8│ 12│ 7│ 11│ 3│ 10 │ │ │ │ │ │ Passeres │ │ │ │ 1│ │ Picariæ │ │ │ │ │ │ Striges │ │ │ │ │ │ Psittaci │ 1│ │ │ │ │ Accipitres │ │ │ │ 1│ │ 1 Columbæ │ │ │ │ │ │ Pterocletes │ │ │ │ │ │ Galli │ │ │ │ 1│ │ 1 Hemipodii │ │ │ │ │ │ Fulicariæ │ │ │ │ │ │ Limicolæ │ │ │ │ │ │ Gaviæ │ │ │ │ │ │ Pygopodes │ │ │ │ │ │ Impennes │ │ │ │ │ │ Steganopodes │ │ │ │ │ │ Tubinares │ │ │ │ │ │ Herodiones │ │ │ │ │ │ Odonotoglossæ│ │ │ │ │ │ Palamedes │ │ │ │ │ │ Anseres │ │ 2│ 1│ 2│ │ 1 Struthiones │ │ │ │ │ │ Crypturi │ │ │ │ │ │ Total Birds │ 1│ 2│ 1│ 5│ 0│ 3 ─────────────┼─────────┼───────┼─────────┼─────────┼───────┼────────── Total │ 9│ 14│ 8│ 16│ 3│ 13 ─────────────┴─────────┴───────┴─────────┴─────────┴───────┴────────── For meaning of italics see foot note Table 1.

The rodents seem to have no power to increase muscle bulk, but a sufficient number of cases of dilatation occur to make one conclude that this is their method of response to unusual strain. Pulmonary disease, mostly of infectious nature, and myocardial degenerations are the principal causes.

The next order to show cardiac enlargement is the Ungulata where nephritis is the most frequent association with hypertrophy and disease of the pleura and pericardium with dilatation, or the reverse of the factor value in the Carnivora. These animals, fairly well prepared for flight, with moderately large hearts, seem more often to show dilatation than hypertrophy.

Two Edentata (armadillo) showed dilatation but no hypertrophy.

Marsupials behave somewhat like rodents in that the heart does not seem to increase muscle bulk, but our records do not explain this clearly. As already mentioned four cases had no sufficient internal reason for dilatation, but as one was probably the result of shock three only remain to be accounted for. Nephritis seemed to exist in all three, but two of them had kangaroo mycosis of the jaw and a general chronic infection.

If now our attention be given to the Aves we find the highly specialized Passeres and Striges not represented and their closely related well- organized orders Picariæ and Psittaci with only an isolated single case. This is the more interesting since the last order suffers reasonably often with arteriosclerosis. Accipitres, the birds of pugnacious habit and carnivorous diet, seem well able to increase their muscle upon demand, but do not often suffer dilatation. Vascular and renal diseases stand out most prominently in the etiology, and one-half of them show myocardial change. The Galli, which includes both ground and flying birds, are represented but fail to exhibit any unusual accompanying disease. Anserine birds apparently have a low power to increase the size of the heart, but most often allow it to dilate. Struthiones, large stalking and rapidly travelling birds, apparently have a good margin of safety in their cardiac mechanism.

SUMMARY OF LESIONS ASSOCIATED WITH HYPERTROPHY AND DILATATION.

Analysis of the associated pathology will reveal that among the mammals, renal disease, chronic infections and diseases of the thoracic serosa are most often responsible for hypertrophy, and that something over one- third of the hearts showed myocardial damage. Among the Aves arteriosclerosis and renal disease are most important in enlarging the heart; half of the cases had myocarditis. In so far as dilatation in mammals is concerned, renal disease and acute infections are decidedly more important than other influences, even than the next in order— chronic infections and pulmonary diseases; only one-fifth of the cases had myocardial disease. Acute infectious disease is the most potent cause of dilatation in birds; only two of the eight cases had degeneration of the heart muscle.

COMPARISON OF MAMMALIA AND AVES.

If a comparison of the incidence of increased muscle bulk in the two classes be made[9] it will be found to occur two and one-half times more often in mammals, while dilatation occurs nearly ten times more often among the mammals than among the birds. Hypertrophy is accompanied by myocardial change in 44 per cent. of the cases, whereas muscular degeneration was only seen in 24 per cent. of the dilatations; this change is conspicuously lacking in the Primates, Ungulates and Marsupials. The usual teaching has been that dilatation, which means enlargement of chambers and thinning of walls or at least no thickening thereof, implied an inability on the part of the heart to keep up with increased demand—a decompensation. If Starling be correct that dilatation is not a degeneration of pump value but merely one of adaptations to increased demand, then this method is more characteristic of mammals than of birds. There is, however, the reserve power to increase the muscle bulk inherent in the mammalian, not possessed or needed by the avian heart. The large-hearted class Aves certainly dilate their blood pump less frequently than mammals and indeed have less cardiac disease.

An analysis of the incidence of hypertrophy _versus_ dilatation shows that hypertrophying power resides in the Primates, Accipitres and Struthiones, their hearts relatively seldom dilatating. Lack of such power and consequent dilatation resides in Rodentia, Ungulata, Marsupialia and Anseres. Hypertrophying power lies therefore chiefly in the heart of average size for its class, dilatation occurring in the small heart. (See page 63.)

AVIAN HYPERTROPHY.

There is little to be learned from the nature and anatomy of the hypertrophies and dilatations except perhaps their character among the birds, in which the physics of the circulation is somewhat peculiar. In this class both the hypertrophy and distention are predominatingly left- sided, a state probably explained by the pressure against which the pump must work in flight because then the lungs and the viscera are somewhat compressed by the pressure of an excess of air in the pneumatic sacs. At all events while concentric hypertrophy was mentioned once, it is difficult to estimate the degree of increase in the right chambers because they are not uncommonly well filled when diastole occurs at death. Grober[10] asserts that the normally large heart (or what I have called “physiological hyperplasia”) shows a “hypertrophy” of the right ventricle because of the extra work entailed in flying. This is certainly not the case in the material we have seen under pathological conditions. Right sided increase might be expected if pulmonary or serous membrane affections were prominent, but left-sided increase, following arteriosclerosis and nephritis is the actual finding. The best examples of concentric hypertrophy are in the dogs with thyroid disease and the best examples of concentric dilatation in ungulates suffering shock.

SUMMARY.

The foregoing pathological data can now be summarized by grouping the facts under the headings of absolute and relative vulnerability of the heart. By the former is meant the actual number and quality of lesions in the various orders, but here at once one comes upon the irregularity of examples of zoological and pathological character, and if one trust entirely to the percentages, fallacious conclusions might be reached. Basing judgment upon the incidence of pathological lesions in mammals and birds, it is evident that the former has greater vulnerability, as 13 is to 6.2. This is noteworthy as we shall learn that the bird has a larger and apparently better prepared heart than the mammal. Attempts to discover the order or kind of animal having the greatest or lowest vulnerability are difficult for the reason given above. Thus, for instance, Pinnipedia, Proboscidea, Edentata, Gaviæ, Impennes, Steganopodes, and Struthiones present the highest percentages of cardiac lesions, but the total specimens examined are so few that these figures may well be misleading. (See Tables 1 and 2.) If, however, figures mean anything in such small groups, these are the animals which have the greatest cardiac vulnerability. They have little in common in regard to zoological relationships and habits; four of the seven orders are rather slothful and three are active. It is much better to limit our observations to those orders from which sufficient examples have been subjected to autopsy and upon which we have some standards for comparison in the heart-body weight ratio. It so happens that in the above seven orders I was unable to obtain any reliable figures of heart weight. Table 3 is a combination of data from Tables 1 and 2 for the principal orders from which we have enough material (at least one hundred autopsies) and for which it is possible to obtain as comparative standards figures indicating the weight of the normal heart in kilograms of body weight; Table 4 gives these ratios for normal hearts. The information about the weights was obtained from some of our own figures and the references given in the footnote.[11] There are no extensive data upon weights and measures in exact terms, such as body weight, so that we are limited to the numbers quoted in parentheses besides the orders in the table. The ratios might be modified slightly by a greater number of examples, but they show certain things by comparison of the classes; in a rough manner the heart ratios correspond to the pathology.

TABLE 3. _Table Containing a Condensation of the Two Foregoing Tables and Showing Figures for Degenerations, Hypertrophy and Dilatations for Orders Having the Largest Number of Autopsies._ ═════════════════╤═════════════════╤═════════════════╤═════════════════ │ Degenerations, │ Hypertrophy │ Dilatation │ &c. │ │ ─────────────────┼─────────────────┼─────────────────┼───────────────── Primates │ 7.6│ .8│ .8 Carnivora │ 11.│ 2.1│ 2.2 Rodentia │ 8.│ 0.│ 4.2 Ungulata │ 5.4│ 1.2│ 3. Marsupialia │ 19.│ .6│ 5. │ │ │ Passeres │ 1.4│ 0.│ 0. Picariæ │ _6.7_│ _1.1_│ 0. Striges │ .8│ 0.│ 0. Psittaci │ 3.4│ 0.│ .1 Accipitres │ 18.3│ 4.3│ .5 Columbæ │ 2.│ 0.│ 0. Galli │ 9.3│ .7│ .7 Herodiones │ 4.1│ 0.│ 0. Anseres │ 15.7│ .6│ 1.5 ─────────────────┴─────────────────┴─────────────────┴─────────────────

TABLE 4. _Table Showing Weight of Normal Heart in Relation to Body Weight. Number of Specimens used to Determine Weight Quoted in Parenthesis._ ════════════════╤═══════════════════════════════ Average Heart of│Grams per Kilogram of Body.[12] ────────────────┼─────────────────────────────── Man ( 4)│ 5.67 Primates ( 4)│ 6.56 Carnivora ( 6)│ 6.78 Rodentia ( 5)│ 5. Ungulata (10)│ 5.8 Marsupialia ( 3)│ 5.1 │ Average 5.82 Passeres (43)│ 19.8 Picariæ ( 9)│ 21.3 Striges ( 4)│ 7.33 Psittaci ( 6)│ 8.89 Accipitres ( 7)│ 12.32 Columbæ ( 4)│ 14.47 Galli (16)│ 11.08 Fulicariæ ( 3)│ 23.82 Limicolæ ( 2)│ 8.78 Anseres (14)│ 11.8 Struthiones ( 1)│ 12.7 │ Average 13.84 ────────────────┴─────────────────────────────── For meaning of italics see foot note Table 1.

However, there are many reasons why great caution should be used in evaluating the relative size of the heart. Welcher showed in his work that the proportion is greater in small and young animals than in large and adult ones. All the authors quoted agree that in birds and to less degree but still clearly in mammals, there is a direct relationship between the bodily activity of an animal and its cardiac bulk. This is fairly well shown in the list of avian heart ratios, but not so clearly in the mammals. What shall be considered the most active mammals—the monkey, perhaps, with his tendency to be occupied constantly, yet we find the greatest heart bulk among the Carnivora, animals prepared for travel and struggle, and the smallest among the Rodentia, quiet and timid animals. The avian order showing the greatest cardiac ratio, the Fulicariæ, shore birds, is made up of some quiet hiding varieties, and of some capable of very prolonged flight; the most constantly active fliers (Passeres) also have a high cardiac weight proportion. The inactive owls have the smallest heart bulk.

The contrast between the average heart-to-body weights of mammals and birds is striking, the latter having two and one-half times as much as the former, 5.8 _vs._ 13.8. Since this is the most prominent and best supported statement in the table of weights, it may be used to compare with the incidence of the pathology as seen in the two classes.

Degenerations and inflammations occur in mammals and birds as 9.5 is to 5.5.[13]

Hypertrophies occur in mammals and birds as 10.3 is to 4.3.[13]

Dilatations occur in mammals and birds as 2.4 is to .28.[13]

In other words, mammals are much more susceptible than birds to degenerative and inflammatory processes, show an ability to increase the muscle bulk two and a half times as great and are liable to chamber distention nearly ten times as often. It might also be put that birds cannot or do not need to increase their muscle, and that the chamber and muscle balance is more perfectly arranged.

While in the preceding pages hypertrophy has been discussed rather from the standpoint of its value as a compensating and reserve capacity, and dilatation as a degenerative or decompensatory process on the part of the cardiac mechanism, it may be that dilatation of the mammalian heart is the usual method employed by the class in response to increased demand. It seems certain, however, that the originally and normally larger heart, both mammalian and avian, more often uses an increase of its muscle to this purpose.

Hypertrophy was accompanied by myocardial disease in 44 per cent. of the cases, while dilatation showed this change in only 24 per cent. This supports the theory that dilatation is a normal response of the myocardium under strain and the belief held in many quarters that the muscle increases its bulk because some of it is damaged.