Carotid Injection Streptococcus mutans in Monkeys1080 MEYERS, RODRIGUES, ANDVASIL S. mutans CR1...
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Vol. 35, No. 3 INFECTION AND IMMUNITY, Mar. 1982, p. 1079-1085 0019-9567/82/031079-07$02.00/0 Fundus Lesions After Carotid Injection of Streptococcus mutans in Monkeys SANFORD M. MEYERS,1'2 MERLYN RODRIGUES,1 AND MICHAEL L. VASIL3* Clinical Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland 202051 and the Departments of Ophthalmology2 and Microbiology and Immunology,3 University of Colorado Health Sciences Center, Denver, Colorado 80262 Received 14 September 1981/Accepted 22 October 1981 Carotid injection of Streptococcus mutans in pigtail monkeys caused fundus lesions clinically resembling those seen in humans with bacteremia. On histopath- ological examination microabscesses occurred in the retina, choroid, and optic nerve. Bacteria were observed in the histopathological sections of the microab- scesses, and S. mutans was cultured from the retina and choroid. Multifocal retinal and choroidal lesions occur after carotid injection of various microorga- nisms: Histoplasma capsulatum in dogs, rab- bits, or monkeys (20, 22, 23), certain bacteria in dogs (14, 15; S. M. Meyers, M. L. Vasil, and L. Yamamoto, Invest. Ophthalmol. Visual Sci., in press), and Cryptococcus neoformans (2) in cats. The present study describes the clinical and histopathological findings after carotid in- jection of a dextran-producing strain of Strepto- coccus mutans in pigtail monkeys and discusses the results in relation to the fundus lesions seen in human cases of bacteremia. The dextran- producing strain of S. mutans used in this study consistently caused fundus lesions after carotid injection in dogs, and altered or diminished dextran production decreased the severity and frequency of the fundus lesions in dogs (14; Meyers et al., in press). Previous investigators have hypothesized that dextrans are of major importance in the pathogenesis of dental caries and some cases of bacterial endocarditis by enhancing bacterial adherence to teeth and dam- aged heart valves, respectively (9, 10, 16, 17, 21). MATERIALS AND METHODS Bacterial strain. S. mutans CR1 is a dextran-pro- ducing strain belonging to serogroup C (kindly sero- typed by W. Bowen, National Caries Program, Be- thesda, Md.) originally isolated from a patient with endocarditis and kindly donated by C. Ramirez-Ronda at the University of Puerto Rico School of Medicine, San Juan (17). Bacteria were maintained by growing them in brain heart infusion broth (Difco Laboratories, Detroit, Mich.), mixing a 12- to 18-h culture 1:1 with sterile skim milk (Difco), and storing them at -70°C. Preparation of a standardized bacterial suspension. Cultures were prepared as previously described (14). Briefly, 30 ml of brain heart infusion broth made with phosphate-buffered saline (pH 6) supplemented with 5% sucrose (grade 1; Sigma Chemical Co., St. Louis, Mo.) was inoculated with 0.1 ml of the skim milk suspension of S. mutans CR1 and incubated without shaking for 16 h at 37°C in 10% CO2. The culture was then centrifuged at 6,000 x g for 15 min, suspended in 30 ml of phosphate-buffered saline (pH 7.2), and blended vigorously in a Vortex mixer for 1 min. The bacterial concentration was -5 x 108/ml as previously determined (14). These culture conditions have been reported as suitable to produce cell-associated dex- trans (17, 21). An indication that the cultures grown in 5% sucrose produced dextrans was their ability to attach to the bottom of the culture flask when grown with sucrose and their failure to attach or adhere without sucrose in the medium. Examination and surgical technique. Seven adult pigtail monkeys, Macaque nemestrina, weighing 7 to 10 kg, were used. The monkeys were sedated with a ketamine (7 mg/kg of body weight)-xylazine (0.6 mg/kg of body weight) mixture given intramuscularly for pre- and postoperative fundus examinations and for fundus photography. General endotracheal anesthesia (2% thiopentol intravenously, nitrous oxide, and halo- thane) was used during the carotid artery surgery. Preoperatively, no fundus lesions were observed by indirect ophthalmoscopy. The eyes were dilated with 2.5% phenylephrine hydrochloride and 1% tropica- mide. A mid-line incision in the neck was made, and the common carotid artery was isolated. The carotid sheath was opened and the branches of the internal and external carotid artery were identified. A 25-gauge needle was inserted into the common carotid artery, and the external carotid artery was clamped transient- ly while a 10-ml suspension of S. mutans was injected over 2 to 3 min. Hemostasis was achieved with firm intermittent pressure. The deep fascial layers and the skin were closed separately with 4-0 and 2-0 polygalac- tin 910 (Vicryl) sutures, respectively. Five monkeys had a 10-ml suspension of S. mutans injected in the right carotid artery and two of these monkeys had similar injections in the left carotid artery 2 to 4 months later. Two monkeys, as controls, had 10 ml of phosphate-buffered saline (pH 7.2) injected into the right carotid artery. Additionally, in dogs, heat-killed 1079 on January 30, 2020 by guest http://iai.asm.org/ Downloaded from
Transcript of Carotid Injection Streptococcus mutans in Monkeys1080 MEYERS, RODRIGUES, ANDVASIL S. mutans CR1...
Vol. 35, No. 3INFECTION AND IMMUNITY, Mar. 1982, p. 1079-10850019-9567/82/031079-07$02.00/0
Fundus Lesions After Carotid Injection of Streptococcusmutans in Monkeys
SANFORD M. MEYERS,1'2 MERLYN RODRIGUES,1 AND MICHAEL L. VASIL3*Clinical Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland 202051 and the
Departments of Ophthalmology2 and Microbiology and Immunology,3 University of Colorado HealthSciences Center, Denver, Colorado 80262
Received 14 September 1981/Accepted 22 October 1981
Carotid injection of Streptococcus mutans in pigtail monkeys caused funduslesions clinically resembling those seen in humans with bacteremia. On histopath-ological examination microabscesses occurred in the retina, choroid, and opticnerve. Bacteria were observed in the histopathological sections of the microab-scesses, and S. mutans was cultured from the retina and choroid.
Multifocal retinal and choroidal lesions occurafter carotid injection of various microorga-nisms: Histoplasma capsulatum in dogs, rab-bits, or monkeys (20, 22, 23), certain bacteria indogs (14, 15; S. M. Meyers, M. L. Vasil, and L.Yamamoto, Invest. Ophthalmol. Visual Sci., inpress), and Cryptococcus neoformans (2) incats. The present study describes the clinicaland histopathological findings after carotid in-jection of a dextran-producing strain of Strepto-coccus mutans in pigtail monkeys and discussesthe results in relation to the fundus lesions seenin human cases of bacteremia. The dextran-producing strain of S. mutans used in this studyconsistently caused fundus lesions after carotidinjection in dogs, and altered or diminisheddextran production decreased the severity andfrequency of the fundus lesions in dogs (14;Meyers et al., in press). Previous investigatorshave hypothesized that dextrans are of majorimportance in the pathogenesis of dental cariesand some cases of bacterial endocarditis byenhancing bacterial adherence to teeth and dam-aged heart valves, respectively (9, 10, 16, 17,21).
MATERIALS AND METHODSBacterial strain. S. mutans CR1 is a dextran-pro-
ducing strain belonging to serogroup C (kindly sero-typed by W. Bowen, National Caries Program, Be-thesda, Md.) originally isolated from a patient withendocarditis and kindly donated by C. Ramirez-Rondaat the University of Puerto Rico School of Medicine,San Juan (17). Bacteria were maintained by growingthem in brain heart infusion broth (Difco Laboratories,Detroit, Mich.), mixing a 12- to 18-h culture 1:1 withsterile skim milk (Difco), and storing them at -70°C.
Preparation of a standardized bacterial suspension.Cultures were prepared as previously described (14).Briefly, 30 ml of brain heart infusion broth made withphosphate-buffered saline (pH 6) supplemented with
5% sucrose (grade 1; Sigma Chemical Co., St. Louis,Mo.) was inoculated with 0.1 ml of the skim milksuspension of S. mutans CR1 and incubated withoutshaking for 16 h at 37°C in 10% CO2. The culture wasthen centrifuged at 6,000 x g for 15 min, suspended in30 ml of phosphate-buffered saline (pH 7.2), andblended vigorously in a Vortex mixer for 1 min. Thebacterial concentration was -5 x 108/ml as previouslydetermined (14). These culture conditions have beenreported as suitable to produce cell-associated dex-trans (17, 21). An indication that the cultures grown in5% sucrose produced dextrans was their ability toattach to the bottom of the culture flask when grownwith sucrose and their failure to attach or adherewithout sucrose in the medium.Examination and surgical technique. Seven adult
pigtail monkeys, Macaque nemestrina, weighing 7 to10 kg, were used. The monkeys were sedated with aketamine (7 mg/kg of body weight)-xylazine (0.6 mg/kgof body weight) mixture given intramuscularly for pre-and postoperative fundus examinations and for fundusphotography. General endotracheal anesthesia (2%thiopentol intravenously, nitrous oxide, and halo-thane) was used during the carotid artery surgery.
Preoperatively, no fundus lesions were observed byindirect ophthalmoscopy. The eyes were dilated with2.5% phenylephrine hydrochloride and 1% tropica-mide. A mid-line incision in the neck was made, andthe common carotid artery was isolated. The carotidsheath was opened and the branches of the internaland external carotid artery were identified. A 25-gaugeneedle was inserted into the common carotid artery,and the external carotid artery was clamped transient-ly while a 10-ml suspension of S. mutans was injectedover 2 to 3 min. Hemostasis was achieved with firmintermittent pressure. The deep fascial layers and theskin were closed separately with 4-0 and 2-0 polygalac-tin 910 (Vicryl) sutures, respectively. Five monkeyshad a 10-ml suspension of S. mutans injected in theright carotid artery and two of these monkeys hadsimilar injections in the left carotid artery 2 to 4months later. Two monkeys, as controls, had 10 ml ofphosphate-buffered saline (pH 7.2) injected into theright carotid artery. Additionally, in dogs, heat-killed
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1080 MEYERS, RODRIGUES, AND VASIL
S. mutans CR1 suspensions did not produce funduslesions (14). All monkeys received 50 mg of hydrocor-tisone intravenously 10 min before the carotid injec-tion and 50 mg of hydrocortisone intramuscularly 2 hpostoperatively. In previous experiments in dogs, hy-drocortisone prevented early postoperative death fromshock but did not affect the nature or severity of thefundus lesions.
Postoperatively, fundus photography and fluoresce-in angiography (0.3 ml of 10% sodium fluoresceinintravenously) were performed in selected monkeyswith a Zeiss fundus flash III camera.
In one monkey, an eye with fundus lesions wasenucleated at 24 h. Under sterile conditions, a swab ofthe retina and choroid in the posterior pole wascultured in brain heart infusion with 5% sucrose, andS. mutans was identified by morphological and bio-chemical characteristics (6).
Histopathology. For light microscopy, the eyes werefixed in buffered Formalin and embedded in paraffin.Sections were stained with hematoxylin-eosin, period-ic acid-Schiff, and the Brown-Brenn technique. Forelectron microscopy, selected tissues were fixed inbuffered glutaraldehyde, postfixed in osmium tetrox-ide, dehydrated in ascending concentrations of alco-hols, and embedded in Epon. Thin sections werestained with uranyl acetate and lead citrate and exam-ined in a Philips 400 electron microscope. A pellet ofcentrifuged microorganisms (S. mutans CR1 culturedas described above) was fixed in glutaraldehyde sepa-rately and processed for electron microscopy.
RESULTSRetinal hemorrhages, white-centered hemor-
rhages, and cotton wool lesions consistentlyoccurred ipsilaterally after all seven carotid in-jections in the five experimental monkeys (Fig.IA). Additionally, one monkey had two smallretinal hemorrhages in the contralateral fundus.The retinal lesions were mainly in the posteriorpole, appeared 2 to 4 h after injection, andreached maximum severity at 1 day. Fluoresceinangiography of the acute fundus lesions exhibit-ed leakage from the retinal vasculature (Fig.IB). In two eyes (the same monkey), fundushemorrhages broke through into the vitreousand obscured the posterior pole but cleared afterseveral weeks. The retinal lesions resolved afterseveral weeks, leaving variable degrees of scar-ring on clinical examination. Occasionally, ede-ma and hemorrhage on the disk (two eyes), faintwhite choroidal lesions without serious retinaldetachment (two eyes), and a mild uveitis (threeeyes) were seen clinically. All five experimentalmonkeys survived without clinically apparentresidual neurological deficits.
Histopathological examination of the acutefundus lesions revealed retinal hemorrhages,clusters of polymorphonuclear leukocytes, withand without surrounding hemorrhage in the reti-na (Fig. 2A), and occasional scattered mi-croabscesses in the choroid, ciliary body, andoptic nerve (Fig. 2C and D).
The Brown-Brenn stain showed gram-positivecocci in the lesions (Fig. 2B and D). Electronmicroscopic examination revealed intra- andextracellular gram-positive cocci resemblingelectron microscopic sections of S. mutans CR1cultured in the same manner as for carotidinjections (Fig. 3 and 4).The culture of the retina and choroid from one
eye with fundus lesions yielded pure cultures ofS. mutans.No fundus lesions occurred in the two mon-
keys which received the phosphate-buffered sa-line control injections.
DISCUSSIONIn monkeys, carotid injection of a cell-associ-
ated dextran-producing strain of S. mutans con-sistently resulted in fundus lesions which clini-cally showed mainly retinal hemorrhages withand without white centers predominantly in theposterior pole of the eye (Fig. 1) and at timeswere accompanied by uveitis and vitreal hemor-rhages. The retinal lesions correlated with mi-croabscesses in the inner retina on histopatho-logical examination (Fig. 2). Occasionally,microabscesses occurred in the choroid, ciliarybody, and optic nerve (Fig. 2). It is of interestthat usually no acute fundus changes were ob-served clinically in the areas of choroidal mi-croabscesses seen histologically. Although thedose of bacteria used in this study was higherthan the range of 103 to 106 organisms per mlreported in certain human gram-positive coccalbacteremias (7), it was necessary to use this highdose to ensure that ocular lesions would occur inall monkeys. For economic reasons, we did notuse other bacteria in monkeys. We used S.mutans CR1 because it had been isolated from ahuman case of endocarditis (17) and was wellstudied in the dog model (14).From this study it appears that the retinal
vascular bed is more prone to bacterial emboli-zation than the choriocapillaries in the monkey,but the explanation for this is not clear. Incontrast, injection of the same strain of S. mu-tans in dogs caused mostly choroidal lesionswith secondary detachment of the retina (15).The inner choroid in the dog tapetal area seemsparticularly vulnerable to bacterial embolizationbecause the choroidal capillaries pass throughthe rigid tapetum (which the monkey lacks) andthen branch off at nearly right angles into thechoriocapillaries (24). Furthermore, the datafrom the dog model reveal that (i) only certainbacteria cause fundus lesions, (ii) heat-killedbacteria do not cause lesions, (iii) pre- andpostoperative antibiotic treatments do not pre-vent or alter the severity of the lesions, and (iv)diminishing dextran production by S. mutansCR1 decreases the frequency and severity of the
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SEPTIC FUNDUS LESIONS IN MONKEYS 1081
-~~~.FIG. 1. (A) Fundus picture showing mild lesions of retinal hemorrhages with and without white centers 24 h
after carotid injection of S. mutans. (B) Moderately severe lesions of retinal hemorrhages with and without whitecenters in macula and optic disk and cotton wool lesions (arrows) 24 h after carotid injection of S. mutans. (C)Fluorescein angiogram of same eye seen in (B) showing leakage of dye in areas of the retinal lesions (arrows).
lesions (Meyers et al., in press). Specifically,Streptococcus sanguis (CR101), coagulase-posi-tive Staphylococcus aureus (ATCC 25923),Streptococcus faecalis (laboratory isolate), andPseudomonas aeruginosa (ATCC 27853 andPA103) consistently caused fundus lesions,whereas free P. aeruginosa toxin, Staphylococ-cus epidermidis (ATCC 12228 and two labora-tory isolates), Klebsiella pneumoniae (ATCC13833 and two laboratory isolates), Escherichiacoli (ATCC 25922), and Proteus mirabilis (threelaboratory isolates) did not cause fundus lesions.These data are likely to apply also to the monkeymodel and, possibly, in some aspects to the
pathogenesis of ocular lesions in humans withbacteremia.The retinal lesions observed in this monkey
model closely resemble the lesions which havebeen described in human cases of bacteremiaunassociated with diabetes mellitus, hyperten-sion, leukemia, or collagen vascular diseases (5,12, 18). The retinal lesions commonly observedin humans have included hemorrhages, cottonwool spots (Roth spots), and white-centeredhemorrhages. However, there has been someconfusion about the exact nature of Roth spots,since they were described by Roth as whitespots in septic cases (18). A few years later,
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1082 MEYERS, RODRIGUES, AND VASIL
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FIG. 2. (A) Representative section of a white-centered retinal hemorrhage 24 h after a carotid injection of S.mutans shows a central cluster of polymorphonuclear cells surrounded by erythrocytes in the inner retina(hematoxylin and eosin; x203). (B) The same lesion in (A) with the Brown-Brenn stain reveals gram-positivecocci (arrows) within the cluster of polymorphonuclear cells (x529). (C) Light micrograph of a choroidalmicroabscess (arrow) without overlying retinal changes (hematoxylin and eosin; x 135). (D) Light micrograph ofa microabscess (arrow) in the optic nerve head area (ON) adjacent to the retina (R) with bacteria present on theBrown-Brenn stain (arrow on inset) (hematoxylin and eosin; x141, inset x529).
Litten described white-centered hemorrhages inbacterial endocarditis and called them Rothspots (12). On histopathological examination,the retinal hemorrhages with and without whitecenters correspond to hemorrhages with andwithout central clusters of polymorphonuclearor mononuclear cells, respectively, in the nervefiber and deeper retinal layers (3, 11, 19). Thecotton wool lesions correspond histologically tocytoid bodies in the nerve fiber layer. In theseclinicopathological studies no bacteria havebeen observed with the Brown-Brenn stain ex-cept for the case reported by Dellman whodescribed a bacterial plug in a retinal capillary(3). Although less frequent than retinal lesions.choroidal lesions have been associated with hu-
man cases of bacteremia. Martyn et al. observedchorioretinal scars on ophthalmoscopic exami-nation in chronic granulomatous disease of chil-dren, a disease in which the polymorphonuclearleukocytes are unable to kill ingested microorga-nisms (13). These chorioretinal scars resemblethose described in dogs after carotid injection ofS. mutans (15). Histopathologically, Dienst andGartner and Friedenwald and Rones describedfoci of choroiditis without overlying retinalchanges in several human cases of bacteremia(4, 8), and Dienst and Gartner also correlatedhyperemia and edema of the optic disk withhistopathological inflammatory foci (4) similar tothe optic nerve microabscesses seen in this study.The data in this study support the hypothesis
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SEPTIC FUNDUS LESIONS IN MONKEYS 1083VOL. 35, 1982
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1084 MEYERS, RODRIGUES, AND VASIL
WA BFIG. 4. Electron micrograph of a pellet of S. mutans showing organisms similar to those in tissues (Fig. 3A
and B). M, Mesosomes (A, x98,040; B, X75,240).
that the fundus lesions observed in human casesof bacteremia result from bacterial emboliza-tion. Of interest in this regard is the recovery ofthe causative bacteria from aspirates of Oslernodes and the finding of dermal microabscesseswith microemboli in nearby arterioles in cases ofbacterial endocarditis (1). These investigatorssuggest that as the skin lesions of bacterialendocarditis (Osler nodes and Janeway lesions)age the host responses destroy the microorga-nisms resulting in inflammation and vasculitis(1). Similarly, bacterial emboli may cause fun-dus lesions in humans, but as the lesions age,bacteria are unlikely to be found on histopatho-logical examination.
ACKNOWLEDGMENTS
This study was supported in part by Public Health Servicegrant EY03069 from the National Eye Institute (to S.M.M.).
We thank L. Yamamoto, R. Gaskins, N. Newman, J.Hackett, and P. Ciatto for their technical assistance.
LITERATURE CITED1. Alpert, J. S., H. F. Krous, J. E. Dalen, R. A. O'Rourke,
and C. M. Bloor. 1976. Pathogenesis of Osler's nodes.Ann. Intem. Med. 85:471-473.
2. Blouin, P., and R. M. Cello. 1980. Experimental ocularcryptococcosis. Invest. Ophthalmol. Visual Sci. 19:21-30.
3. DeUman, F. 1919. Metastatische Prozesse am Auge bieEndocarditis lenta. Klin. Monatsbl. Augenheilkd. 63:661-671.
4. Dienst, E. C., and S. Gartner. 1944. Pathologic changes inthe eye associated with subacute bacterial endocarditis.Arch. Ophthalmol. 31:198-206.
5. Duke-Elder, S., and J. H. Dobree. 1967. Septic retinitis, p.208. In S. Duke-Elder (ed.), Systems of ophthalmology,diseases of the retina, vol. 10. C. V. Mosby Co., St.Louis, Mo.
6. Finegold, S. M., W. J. Martin, and E. G. Scott. 1978.Facultative streptococci, p. 135. In W. R. Bailey and E.G. Scott (ed.), Diagnostic microbiology. C. V. MosbyCo., St. Louis, Mo.
7. Finegold, S. M., M. L. White, I. Ziment, and W. R. Winn.
INFECT. IMMUN.
ma
on January 30, 2020 by guesthttp://iai.asm
.org/D
ownloaded from
SEPTIC FUNDUS LESIONS IN MONKEYS 1085
1969. Rapid diagnosis of bacteremia. Appl. Microbiol.18:458-463.
8. Friedenwald, J. S., and B. Rones. 1930. Some ocularlesions in septicemia. Trans. Am. Ophthalmol. Soc.28:286-300.
9. Gibbons, R. J., and R. J. Fitzgerald. 1969. Dextran-induced agglutination of Streptococcus mutans, and itspotential role in the formation of microbial dental plaques.J. Bacteriol. 98:341-346.
10. Gould, K., C. H. Ramirez-Ronda, R. K. Holmes, and J. P.Sanford. 1975. Adherence of bacteria to heart valves invitro. J. Clin. Invest. 56:1364-1370.
11. Kennedy, J. E., and G. N. Wise. 1965. Clinicopathologiccorrelation of retinal lesions, subacute bacterial endocar-ditis. Arch. Ophthalmol. 74:658-662.
12. Litten, M. 1878. Veber akute maligne Endocarditis unddie dabei vorkommenden Retinalveranderungen. ChariteAnn. 3:135.
13. Martyn, L. J., H. W. Lischner, A. J. Pileggi, and R. D.Harley. 1972. Chorioretinal lesions in familial chronicgranulomatous disease of childhood. Am. J. Ophthalmol.73:403-418.
14. Meyers, S. M., and M. L. Vasil. 1980. Septic choroiditiswith serous retinal detachment in Streptococcus mutans-injected dogs. Infect. Immun. 29-.714-718.
15. Meyers, S. M., J. P. Wagnild, I. H. L. Wallow, R. Klein,G. de Venecia, J. C. Allen, and E. M. Lapinski. 1978.Septic choroiditis with serous detachment of the retina indogs. Invest. Ophthalmol. Visual Sci. 17:1104-1109.
16. Mukosa, H., and H. D. Slade. 1973. Mechanism of adher-
ence of Streptococcus mutans to smooth surfaces. I.Roles of insoluble dextran-levan synthetase enzymes andcell wall polysaccharide antigen in plaque formation.Infect. Immun. 8:555-562.
17. Ramirez-Ronda, C. H. 1978. Adherence of glucan-positiveand glucan-negative streptococci strains to normal anddamaged heart valves. J. Clin. Invest. 62:805-814.
18. Roth, M. 1872. Ueber Netzhautaffectionen bei Wundfie-bern. Dtsch. Z. Chir. 1:471-480.
19. Roth, M. 1872. Beitrage zur Kenntnis der varicosenHypertrophie der Nervenfasern. Virchows Arch. A55:197-217.
20. Salfelder, K., I. Schwarz, and M. Akbarian. 1965. Experi-mental ocular histoplasmosis in dogs. Am. J. Ophthalmol.59:290-299.
21. Scheld, W. M., J. A. Valone, and M. A. Sande. 1978.Bacterial adherence in the pathogenesis of endocarditis.Interaction of bacterial dextran, platelets, and fibrin. J.Clin. Invest. 61:1394-1404.
22. Smith, R. E., J. I. Macy, C. Parrett, and J. Irvine. 1978.Variations in acute multifocal histoplasmic choroiditis inthe primate. Invest. Ophthalmol. Visual Sci. 17:1005-1018.
23. Smith, R. E., G. R. O'Connor, C. J. Halde, M. A.Scalarone, and W. M. Easterbrook. 1973. Clinical coursein rabbits after experimental induction of ocular histoplas-mosis. Am. J. Ophthalmol. 76:284-293.
24. Walls, G. L. 1942. The tapetum, p. 234. In J. J. Head (ed.),The vertebrate eye. The Cranbrook Press, BloomfieldHills, Mich.
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