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VENEREALSPIROCHETOSISIN AMERICANRABBITS.

BY I-IIDEYO NOGUCI-II, M.D.

(From the Laboratories of The Rockefeller Institute for Medical Research.)
PLATES17 TO20.
(Received for publication; November 10, 1921.)
Ross, 1 in 1912, in a discussion of an intracellular phase of Treponema pallidum,
mentioned a disease of rabbits characterized by chancres, buboes, ulcers on the
genitals, mouth, anus, etc., in which he reported finding cell inclusions in themononuclear leucocytes similar to those which he had found in human syphilis.
He suspected that there might be a spiral phase of the parasite of the rabbit disease, and Bayon~ undertook the examination of the genital lesions, in which
he found a spiral organism indistinguishable from Treponema pallidum:
Similar lesions appeared in other rabbits 25 days after inoculation of the material
containing the spiral organism. Bayon described the rabbit spirochete as being
about one and a half times the diameter of a blood corpuscle in length, having
5 to 8 closely set, deep, rather elastic curves, and showing rotating but not lashing
movements. He remarked that students of experimental syphilis in the rabbit
should take note of the presence of this new species of Treponema.
Arzt and Kerl, 3 in 1914, reported finding in a peculiar scaly, papular, or erosive
lesion, with crust, around the anogenital region of apparently normal rabbits,
spiral organisms morphologically indistinguishable from Treponema pallidum.
Of 850 rabbits examined by them, 26.9 per cent showed the same organism, andin one series of 189 adult rabbits the spirochetes occurred in 34.4 per cent. Arzt
and Kerl transmitted the spirochetal affection by applying to the scarified vulva or
prepuce of normal rabbits the exudate from the lesion of a rabbit showing the
spontaneous disease. After several weeks incubation, the inguinal lymph nodes
became somewhat enlarged, and the spirochetes appeared. Similar lesions oflips and clitoris showed the spirochete in large numbers. Intratesticular inoculations were unsuccessful, possibly because of the contaminated nature of thematerial, and inoculations into the scarified eyebrows of two monkeys were
negative.
1 Ross, E. H., An intracellular parasite developing into spiroch~etes, Brit. Med.
Y., 1912, ii, 1653.
Bayon, H., A new species of Treponema found in the genital sores of rabbits,
Brit. Med. J., 1913, i.i, 1159.
8 Arzt, L., and Kerl, W., Weitere Mitteilungen fiber Spiroch~ttenbefunde bei
Kaninchen, Wien. klin. Woch., 1914, xxvii, 1053.
391

392

VENEREALSPIROCII-ETOSIS IN AM'V.RICAIq R A B B I T S

With a view to differentiating between this organism and Treponema pallidum,
Arzt and Kerl3, 4 inoculated the testicle of a rabbit suffering from the disease inquestion with a strain of Treponema pallidum. The inoculation was successful, butsince a syphilitic rabbit can be superinfected or doubly infected, as shown by Truffi, sand by Uhlenhuth and Mulzer, n no conclusion was drawn. No importance
was attached to the Wassermann reaction, and an attempt to employ as antigen
in a complement deviation test tissue from syphilitic orchitis of the rabbit failed.
Examination of certain stocks in Innsbruck, ~ where no experimental workon syphilis in the rabbit had ever been done, showed the same disease to prevail.
Similar observations were made on Hamburg rabbits by Jacobsthal in 1920. 8
The lesions present were situated on the vulva and were of a squamous, erosive
kind. The dark-field microscope revealed, in the lesions and in the vaginal secretion, numerous spirochetes resembling pallidum. ]acobsthal thought the spiralorganism to be a trace thicker than pallidum and not to exhibit the undulatory
movements so characteristic of the latter. Transmission experiments with miceand guinea pigs were negative, but lesions were reproduced in female rabbits inthree instances by scarification of the vulva, after an incubation period of 3 to 6
weeks. A chancre-like lesion was noted in one animal. He proposed callingthe disease paralues cuniculi and the organism Spiroctt~eta paraluis cunlculi. 9
Later in 1920, Schereschewsky1° stated that the peculiar lesion of the rabbit
disease is of papular and ulcerative form and is transmitted by coitus, the incubation period varying from 14 to 30 days.
In 1921 Klarenbeek n observed spirochetal lesions in five Dutch rabbits. Inoculations of the spirochete-containing material by scarification into the perineal
4Arzt, L., Spirochgtenbefunde in Genitalver~inderungen ungeimpfter Kaninchen, Dermat. Z., 1920, xxix, 65.
~Truffi, M., Ueber die Empfiinglichkeit des Kaninchens gegeniiber syphilitischen Relnfektionen, Cenlr. Bakl., lte Abt., Orig., 1910, ]iv, 337.
6 Uhlenhuth, P., and Mulzer, P., Beitr~ige zur experimentellen Pathologic undTherapie der Syphilis mit besonderer Berficksichtigung der Impf-Syphilis derKaninchen, Arb. k. Gsndhlsamte, 1913, xliv, 307.
rArzt, L., and Kerl, W., Zur Frage der "Kaninchensyphilis," Dermal. Woch.,
1920, lxxi, 1047.
8Jacobsthal, E., Untersuchungen fiber eine syphilis~hnliche Spontanerkrankung des Kaninchens (Paralues cuniculi), Dermal. Wock., 1920, hxi, 569.
9 Arzt and Kerl 7 remind Jacobsthal that neither incubation time nor histologicalchanges of the lesion warrant the differentiation of this disease from experimental
syphilis in rabbits.
10 Schereschewsky, J., Geschlechtlich tibertragbare origin~ire Kaninchensyphilis
und Chinin-Spiroch/itotropie, Berl. klin. Woch., 1920, lvii, 1142.
11Klarenbeek, A., Recherches exp~rimentales avec un spirochete, se trouvant
spontan6ment chez le lapin et ressemblant au Treponema pallidum, Ann. Inst.
Pasteur, 1921, xxxv, 326.

m~Yo~oovc~

393

region of normal rabbits gave rise, 11 days later, to a slightly excoriated hyperemic
reaction without induration, while on the scarified dorsal skin superficial lesions
with white crust appeared after 1 to 2 months incubation. The lesions showedspirochetes. Intraocular inoculations in rabbits resulted in some instances in an
ulcer on the upper lid and a keratitis after 41 to 43 days; intratesticular inoculations failed to give any spirochetal orchitis.

Spontaneous Instances in America.
T h e facts reviewed in the foregoing p a r a g r a p h s suggested thee x a m i n a t i o n of A m e r i c a n rabbits. T h e s a m e condition has beenfound a m o n g the stock rabbits a t T h e Rockefeller I n s t i t u t e . Of
50 rabbits examined in June, 1921, three females and two males were
found to h a v e lesions on t h e vulva, prepuce, and perineum. One(No. 3) of t h e female r a b b i t s was b o r n a t T h e Rockefeller I n s t i t u t e
6 years ago, has been k e p t as normal breeding stock ever since, andhas never b e e n used for a n y e x p e r i m e n t a l work.
R e c e n t l y ( N o v e m b e r , 1921) six females with similar lesions h a v ebeen found a m o n g t w e n t y r a b b i t s just p u r c h a s e d in P e n n s y l v a n i a .

Rabbit/.--Adult female; used for breeding purposes for several months.
June 29, 1921. Scaly ulcerative lesions covered with grayish white crusts present
on both sides of vulva (Fig. 38). Upon removal of the crusts with forceps, agranular, easily bleeding surface was exposed. The crust and scrapings fromthe exposed ulcer both revealed the presence in fairly large numbers of a spiralorganism resembling Treponema pallidum (Figs. 1, 13, and 17). The lesions persisted without much change in extent and character up to the last examination(Sept. 26, 1921). Spirochetes were still numerous. Tissue was removed on June29, 1921, for inoculation and histological studies. The animal was sacrificed on
Sept. 27, and the lymphatic glands were examined for the spirochetes.
Rabbit 2.--Adult nursing female. June 30, 1921. Found to have small, scaly,rather dry lesions on both sides of the vulva; no ulceration. Scrapings examinedby dark-field microscope showed in small numbers spirochetes resembling pallidum. The lesions remained unchanged up to the last examination (Oct. 13,
1921), but spirochetes were more numerous at that time. The three young
rabbits remain entirely free from any lesion, although kept with the mother during
a period of 3 months.
Rabbit 3.--Adult female; born at The Rockefeller Institute in 1915 and kept
as breeding stock since. June 30, 1921. Scaly, papular elevation or thickeningof the vulval region on both sides (Fig. 39), covered by thin grayish crusts overthe center of the hyperemic lesions. Examination for spirochetes revealed one fine394

VENEREAL SPIROCI-IETOSIS IN AMERICAN RABBITS

type in enormous numbers (Figs. 2 to 4, 14, 15, and 18 to 20) and another decidedly
coarser type in smaller numbers (Figs. 5, 6, and 27 to 29). Tissue was excisedon June 30, and July 15, 1921, for section and for inoculation. On July 20, 1921,
there was no perceptible change in the lesion, and numerous spirochetes were stillpresent (Figs. 9 to 11). This animal was later treated with salvarsan (see below).
Rabbit 4.--Normal adult male; recently purchased. July 6, 1921. Presented
small congested and quite swollen but not indurated lesions of the prepuce (Fig.
40), covered with thin crusts; the lesions bled easily when the crusts were removed.
The dark-field microscope showed numerous spirochetes similar to those found in
the other animals (Figs. 7, 8, 16, and 21 to 24). On July 20, 1921, there were still
spirochete-containing lesions. Toward the end of September scaly papularlesions were noticed on nose and lips (Fig. 42), eyelid (Fig. 43), and paws (Fig.
44), and the spirochetes were found to be present there also.
Rabbit 5.--Normal adult male; recently purchased. Sept. 10, 1921. Prepuceswollen and covered with grayish thin scales, under which the tissue was granular,soft, somewhat edematous, and congested (Fig. 41). Numerous spirochetes
present. Lesion excised for histological examination.

Spirochetes.
The type of spirochete existing in the lesions of the five rabbits
just described closely resembles Treponema pallidum. The measurements are: length 10 to 16 ~; width 0.25 u. The spiral amplitude,
in regular portions, is about 1 to 1.2 ~, and the spiral depth 0.6 to
1 u; hence the number of spirals in an individual measuring 10 u m a ybe about 9 or 10. The last spirals near the extremities are often
shallower t h a n those of the middle portion or "vice versa, and the ends
are sharply drawn. A delicate terminal filament has been seen atone, and sometimes at both ends. The shortest specimens measured
7 #, with 6 spirals, and the longest about 30 u, with 25 to
28 spirals (Fig. 4). The average is about 12 to 14 u (Figs. 3,5, and 6), the organism being slightly longer t h a n the pallidum inh u m a n lesions. In experimentally inoculated rabbits specimens ofpallidum as long as 24 u m a y be encountered, but the single length isusually 10 to 12 u (Figs. 12 and 32 to 34). As in the case of pallidum(Figs. 35 to 37), specimens with stretched spirals appear in stained
preparations (Figs. 25 and 26).
In the lesion of Rabbit 3 there were present two types of spirochete,
one the usual fine type and the other decidedly coarser than the
average. The morphology of the coarser variety suggests t h a t of

HmEYO NOCVCm

395

Treponema calligyrum found by the writer in the human condyloma,TMbut it is somewhat longer than calligyrum (14 to 18 ~, width 0.35 tz).
The spiral amplieude is 1.2 to 1.75 u and the spiral depth 0.6 to 1.5(Figs. 6 and 27 to 29). This form is perhaps a trace thinner andlonger than the calligyrum, or medium type smegma treponema of
the normal human genitalia. The organism rotates actively, withoccasional bending at the middle, but no vibratory or lashing movements have been observed.
The rabbit treponema forms entangled masses of long threads,
30 u at least (Figs. 4 and 11), a phenomenon I do not recall having seenin the case of Treponema pallidum. T h e agglomeration of organisms
in a striking stellate mass of several to a dozen individuals is frequently
observed (Fig. 10). A similar behavior has been observed in young,
actively motile, pure cultures of Treponema pallidum. Both pallidum
and the rabbit treponema sometimes form a ring by touching one
end with the other while actively rotating, and occasionally they
make a knot of themselves. In a film preparation from the lesions ofRabbit 3, stained by Fontana's method, occasional wavy, but not
spiral forms were seen; perhaps they were degenerated or involution
forms (Figs. 30 and 31).
The staining properties of these rabbit spirochetes are the same as
those of Treponema pallidum. Both can be readily stained by ordinary basic aniline dyes when fixed in a buffered formaldehyde solution,
as shown by Miss TildenY Jacobsthal proposed for the organism
the name Spirochceta paraluis cunlculi, but in view of its close resemblance to Treponema paUidum and Treponema pertenue it m a yperhaps be more appropriate to use the simpler name Treponema
cuniculi.
Examinations of smegma and mucous secretions on the genitalia
of many normal male and female rabbits failed to reveal any spirochetal organisms, which circumstance does not of course exclude thepossibility that spirochetes are occasionally present in such materials.
t~ Noguchi, H., Cultivation of Treponemacalligyrum(new sp6cies) from condylomata of man, Y. Exp Med., 1913, xvii, 89.
x3Noguchi, H., A note on the venereal spirochetosisof rabbits. A new technic
for staining Treponeraapallidum, J. Am. Med. Assn., 1921, lxxvii, 2052.

396

VENER.~AL SPIROCHETOSIS IN A M E R I C A N RABBITSHistology of the Lesions.
Excised tissue from the undisturbed spontaneous lesion on the
prepuce of Rabbit 5 (Fig. 41) was fixed in Zenker's fluid and sections were stained with hematoxylin-eosin and eosin-methylene
blue. The epidermis was thickened and the papillm were large
and prominent; the infiltration was spotty and mainly confined tothe interpapillary layers. The new cells were mainly mononuclear,partly eosinophils, and few or no polymorphonuclears were present.
In general features the lesion suggests a condyloma. Although certain blood vessels were surrounded by mononuclear cells, no definite
endothelial proliferation was apparent (Fig. 48). The lesion as
described may be taken as the pure type before secondary bacterial
infection has come in to induce acute inflammation and mar the picture. Once ulceration has taken place, as in the vulval lesions ofRabbits 1 and 3 (Figs. 38 and 39), the interpapillary infiltration ofmononuclear cells is accompanied by numerous polymorphonuclear
leucocytes, which invade also the stratified layers of the thickened
epidermis. Minute hemorrhages and necrotic foci are then occasionally met with.
For comparison with these lesions, a scrotal chancre was inducedwith the Nichols strain of Treponema pallidum long adapted to therabbit (since 1912). The chancre on the 28th day was indurated andstood out as an oval mass from the surrounding loose connective tissue(Fig. 47); in histology it differed widely from the genital lesions inducedby the rabbit spirochete. The corium was highly infiltrated withmononuclear cells, some showing eccentric nuclei and checker-board
chrornatin. Polymorphonuclear leucocytes were absent. But the
striking difference was in the blood vessels, which were surroundedby the new cells (Fig. 49).
Repeated attempts to stain the spiral organism in the tissue bymeans of silver impregnation have been only partially successful.
The organisms near the surface of the lesion took the stain. By
careful teasing of the deeper layers and dark-field examination,
spirochetes have been found to be present in all parts of the lesions.

ma)xYo ~oo~¢m

397Transmission Experiments.
First Passages.--Sixteen rabbits and four monkeys1. (Macacus
rhesus) were inoculated with the material containing the spirochetes,
usually on the scarified prepuce or vulva. In rabbits some intratesticular, intracorneal, and intraocular inoculations were made; inmonkeys the scarified eyebrows, as well as prepuce or vulva, were
smeared with the scraping of the rabbit lesion. Each of the original
rabbits was paired in a separate cage with a normal rabbit of opposite
sex for the purpose of sexual transmission.
Reproduction of the disease on the vulva or prepuce respectively
was obtained in all five of the female and in eight of the elevenmale rabbits inoculated (Table I). One strain (Rabbit 3)produced
in two male rabbits a superficial scaly, papular lesion on the scrotalskin at the site of testicular inoculation (Fig. 45), and in one of thema lesion developed also on the prepuce. The results of intratesticular
inoculation were in general unsatisfactory. In most cases, owing to
the impure nature of the material, a more or less acute suppurativeorchitis ensued, and no spirochetes were present in these lesions.
Negative results also followed intraocular and intracorneal inoculations and the application of the material to the scarified surface ofthe cornea. The lymph glands were not noticeably enlarged either
in the original rabbits or in those inoculated. The inoculation ofemulsions of popliteal and inguinal lymph glands from ten rabbits
infected with Treponema cuniculi into both testicles of four normal
male rabbits did not produce any orchitis within 3 months. On theother hand, similar emulsions from rabbits infected with Treponema
pallidum gave rise to typical orchitis within 1 month.
24Four additional monkeys were later inoculated with different strains of Treponema cuniculi, but none showed any lesion during a period of observation of 3
months. In order to determine whether,the adaptation to rabbits of the humanstrain of Treponernapallidum had rendered it avirulent for monkeys, two monkeys were inoculated with the Nichols strain (1912). Both presented typicallesions within 1 month. Two monkeys inoculated from a case of human chancre
showed typical lesionswithin 2 months. The pathogenicity of Treponemacunivu/i appears, therefore, to be different from that of Treponemapalliduraof humansyphilis.

398

VENEREAL SPIROCHETOSIS IN AMERICAN RABBITS

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402

V~N~REAL SPIROCtt~TOSIS IN P,M-ERICAI~ RABBITSThe period of incubation varied from 20 to 88 days, the average
being 60{ days.
Subsequent Passages.--All five strains are being maintained in rabbits. The strain from Rabbit 1 has now passed through four transfers: first, June 30, 1921, positive September 13 (75 days); second,
September 27, positive October 17 (20 days); third, October 17,
positive October 22 (5 days); fourth, October 24, positive November
10 (17 days).
Inoculations of monkeys have remained up to the present (4 months)
without result. One of the monkeys was inoculated with two different
strains, on right and left eyebrow respectively. Two other monkeys
have recently been reinoculated in the eyebrow, and also into the
hypogastric region, with a hypodermic needle, the infective material
being deposited intradermally.
Sexual Trammission.--Rabbit 1 was kept in the same cage withthree males successively (July 12 to September 26), Rabbit 2 withtwo males, and Rabbit 3 with one male (July 12 to October 15). Rabbit 22, 3 months after having been placed with Rabbit 3, showed asmall papular lesion on the prepuce in which spirochetes were numerous.
Attempts to Produce Chancre on the Scrotum.

Treponema pallidum from human syphilis is capable of producing
chancre-llke lesions on the scrotum of rabbits when a small piece ofpallidum-containlng tissue is subcutaneously introduced (Tomasczewski,15 Uhlenhuth and Mulzer, e Brown and Pearce, le and others).
To determine whether or not the rabbit spirochete is capable of producing a similar lesion in rabbits, portions of the erosive, spirochetecontaining lesion from the vulvolabial region of Rabbit 3 were introduced into the subcutaneous pocket of each of the scrota of two
adult male rabbits, two other adult males being simultaneously inoculated with fragments of freshly excised scrotai chancre from asyphilitic rabbit (Nichols strain).
1~Tomasczewski, Ueber eine einfache Methode, bei Kaninchen Prim~iraffektezu erzeugen,Deutsch. reed. Woch., 1910,xxxvi, 102S.
16Brown, W. H., and Pearce, L., Experimental syphilis in the rabbit. II.
Primary infectionin the scrotum. Part 1. Reactionto infection, J. Exp. Med.,
1920, xx~o 709.

HIDE¥O NOGUC~403

One of the rabbits (No. 23) inoculated with the rabbit spirochete
showed at one site of insertion after 27 days a small crust under which
the surface was soft, pale, and granular, but there was no marked
induration. Spirochetes were not found in the lesion until 45 days
after inoculation. The other site remained small and reddish, witha trace of infiltration, but no spirochetes were found. The otherrabbit (No. 24) showed slight infiltration at one site of insertion(Fig. 46), but no definite, chancre-like induration developed during 2
months observation. Brownish scaly patches rich in spirochetes
appeared on the right scrotum after 45 days.
Of the two syphilitic controls, Rabbit 25 developed within 3 weeks
at the site of insertion on the right scrotum a typical chancre which
attained a diameter of 2 cm. in 28 days (Fig. 47). The second control (Rabbit 26) had not developed a chancre 75 days after inoculation. Two rabbits inoculated with chancre material from Rabbit
25 developed typical chancres within 3 weeks, while simultaneous
inoculations from the slightly indurated (cuniculi) lesion of Rabbit
23 were unsuccessful.
It is possible that a chancre may yet be produced with the rabbit
spirochete by inoculation of a large number of animals. The numberof spirochetes in the pallidum chancre of rabbits is never as large asthat found in the cuniculi lesions in rabbits.
For the purpose of comparison, pallidum-containing material wasapplied to the scarified prepuce or vulva of rabbits and gave rise tochancre-like nodules. The appearance of these lesions, however, wasentirely different from that of the lesions produced by Treponema

cuniculi.
Typical cuniculi lesions may be produced on the scrotal skin or prepuce of rabbits having active pallidum lesions, and the reverse is also
true. The infections appear to follow independent courses.

Wassermann Reaction.
The sera of the eleven rabbits with spontaneous lesions, and of
thirty-three experimentally inoculated from them, have been tested
for the Wassermann reaction. The acetone-insoluble lipolds served
as antigen, and the inactivated sera were used in quantities of 0.1
and 0.2 co. Twenty-four of the animals had active, spirochete-

404

VENEREALSPIROCHETOSISIN" ~ R I C A I q

RABBITS

containing lesions of the genital region at the time of test; twenty had
recently been inoculated and had not developed any lesions. The
results of the tests were uniformly negative.
The sera of four rabbits having active scrotal chancres (Nichols
strain of Treponema pallidum) were simultaneously tested; three gavea strongly positive ( + + + + ) , and the other a partial ( + ) reaction.
Twelve rabbits which had developed chancres 2 months after inoculation on vulva or prepuce with pallidum gave strongly positive( + + + + ) reactions.
Thus far positive Wassermann reactions have been obtained onlywith the sera of rabbits having active syphilitic lesions. Apparently
no complement-fixing substance, such as exists in the blood of syphilitic human beings or experimentally infected syphilitic rabbits, waspresent in the blood of animals which had been infected with the
rabbit treponema for periods varying from 1 or 2 weeks to many
months. Whether or not the fixing substance will eventually appear
in the sera of these rabbits remains to be seen.

Effect of Salvarsan.
Rabbit 3 was given intravenously on August 17, 1921, 0.02 gin.
of salvarsan per kilo of body weight. Rabbit 27, having a chancreof thumb size on each scrotum, was similarly treated at the sametime to serve as control.

Rabbit 3.--Aug. 17, 1921. Showedpapuloedematous, partially eroded, moist
lesion, extending over the entire vulval region, including the labial mueosa andadjacent skin; perineum also scaly, congested, and swollen. Dark-field examination revealed spirochetes in large numbers. 5 p.m. 4.4 cc. of a 1:10 dilutionof slightly alkaline salvarsan solution was intravenously administered (0.02 gin.
per 1,000 gin. of body weight). Aug. 18, 5 p.m. Considerable reduction in
swelling, less irritation, apparent drying up of lesion; no spirochetes found. Aug.
20. Lesionnear hair line of vulva still somewhat moist and crusted, inferior portion practically healed; anal lesion still present. Spirochetes were no longer foundin any of the suspicious spots. Aug. 26. Only small scabs present. Sept. 13.
Slight scaliness at hair line of vulva; no spirochetes.
Rabb#27.--Aug. 17, 1921. Chancre (human strain isolated by Nichols in 1912,
since maintained in rabbits) on each scrotum, 2 cm. in diameter; cartilaginous
induration, with small umbilicated center covered by dark dry crust. Many

Hm~YO NOGUCm

405

spirochetes present. 5 p.m. 5 cc. of a 1 : I0 dilution of slightly alkaline salvarsan(0.02 gin. per 1,000 gm. of body weight) intravenously admln{~tered. Aug. 18.
Lesions softer, smaller; no spirochetes. Aug. 20. Lesions soft. Aug. 23.
Lesions have almost disappeared. Sept. 13. No trace of lesions found.
The experiment indicates that the cun~uli lesions and the experimental scrotal chancre caused by Treponema pallidum from humansyphilis are similarly influenced by salvarsan. In both instances the
spirochetes disappeared within 24 hours after the administration of
the drug, and the lesions themselves within 9 days. No recrudescence has occurred.
DISCUSSION AND SUMMARY.
Of 50 rabbits, otherwise regarded as normal, three adult females
and two adult males (10 per cent) have been found to have in theirgenitoperineal region certain papulosquamous, often ulcerating, lesions. A recently purchased group of twenty rabbits contained six
females (30 per cent) with similar lesions. This condition runs achronic course and is characterized by the presence of a spiral organism
closely resembling Treponema pallidum.
The rabbit spirochete has the same morphological features as
Treponema pallidum; it is possibly a trifle thicker and longer than the
average pallidum. Long specimens measuring 30 u are frequently
encountered, and they show a tendency to form loosely entangled
knots. A stellate arrangement of several organisms in a mass isfrequently observed.
In the lesion of one rabbit there were two types of spirochete, oneof the variety just described, the other a somewhat coarser organism,
closely resembling Treponema calligyrum found in a human condyloma, but a trifle thinner and longer. This organism is perhaps
merely a variant type of the rabbit spirochete.
The histological reactions are similar to, but considerably lesscellular, than those occurring in typical primary syphilitic lesions.
There is a marked hyperkeratosis and interpapillary infiltration notobserved in scrotal chancre.
The disease is transmissible to normal rabbits, in which the usual
papular lesions can be readily reproduced in the genitoperineal region. In the first passages the incubation period varied from 20 to406

VENEREALSPIROCHETOSIS IN AM3~.RICA_N RABBITS

88 days; subsequently one of the strains produced a lesion in 20 dayson the second, and in 5 days on the third passage. No typical orch/tis or keratitis was produced fix the rabbits of the present series,
although in one of the original rabbits (No. 4) scaly, papular lesions
have developed on the nose, lips, eyelid, and paws. Monkeys (Macacus rhesus) failed to show any lesions within a period of 4 months
after inoculation.
In one instance transmission was accomplished through the mating of an infected female with a normal male.
The Wassermann reaction was uniformly negative in the fiverabbits with spontaneous lesions and in eighteen rabbits experimentally infected.
Salvarsan had the same therapeutic effect on the lesions producedby the rabbit spirochete as on the experimental pallidum lesion of the
rabbit.
The organism belongs to the genus Treponema, and may bedesignated Treponema cuniculi.
EXPLANATIONOF PLATES.

PnA~E 17.

Dark-field photographs.

Magnification X 1,000.

FIG. 1. Treponemacuniculi from Rabbit 1.
FIGS. 2 to 5. Treponema cuniculi from Rabbit 3. Fig. 4 shows one of thevery long specimens.
FIG. 6. The coarser type of treponema from Rabbit 3.
FIGS. 7 and 8. Treponema cuniculi from Rabbit 4.
FIGS. 9 to 11. Treponema cuniculi from Rabbit 3. Fig. I I shows an entangled
mass of the long forms. Fig. 10 illustrates the agglomeration of organisms instellate form which is frequently seen.
FIG. 12. Treponema pallidura from experimental syphilitic orchitis in the rabbit.
PLATE 18.
Magnification × 1,000.
FIG. 13. Film preparation of exudate from Rabbit 1, stained with Giemsa
solution.
FIGS. 14 and 15. Film preparation of exudate from Rabbit 3, stained with
Giemsa so]ution.
FIG. 16. Film Dreparation of exudate from Rabbit 4; Giemsa stain.
Fro. 17. Fil¢ t )aration fron'r Rabbit 1, stained by Fontana's method.

HrDEYO NOOVCm

407

FIGS. 18 to 20. Film preparation from Rabbit 3, stained by Fontarm's method.
FIGs. 21 to 24. Film preparation from Rabbit 4, stained by Fontana's
method.
FIOS. 25 and 26. Irregular forms of Treponemacuniculi from Rabbit 3, stainedby Fontana's method.
FIGS. 27 to 29. Spirochetes resembling Treponema calllgyrum from Rabbit 3,
stained by Fontana's method.
FlOS. 30 and 31. Non-spiral forms from Rabbit 3.
FIGs. 32 and 33. Treponemapallidum in rabbit orchitis, stained by Fontana's
method.
Fio. 34. TreponemapaIlidum in rabbit orchitis. Mordant Gentian violet.
FIos. 35 to 37. Irregular forms of Treponema pallidum from experimental
scrotal chancre, stained by Fontana's method.
PLATE 19.

FI0S. 38 to 41. Typical lesions (from Rabbits 1, 3, 4, and 5 respectively) on
the rabbit genitalia.
FIG. 42. Lesions in Rabbit 4 on the nose and left upper lip.
Fio. 43. The same, on the left eyelid.
FIG. 44. The same, on the left paw near the joints of the nails.
FIG. 45. An erosive lesion at the site of intratesticular inoculation in Rabbit 18(transfer from No. 3) after an incubation period of 49 days. There was onlya slight induration, but numerous spirochetes were present.
FIG. 46. The healing scar in Rabbit 24 at the site of pocket insertion of theinfective material in the unsuccessful attempt to produce chancre (photographtaken 28 days after inoculation). Treponemacuniculi found after 73 days.
FIG. 47. A typical chancre, for comparison, on the scrotum of Rabbit 25, inoculated with the Nichols strain of Treponema pallldum Note the cartilaginous,
well circumscribed, umbilicated chancre (photographed 28 days after insertion).
PLATE 20.

FIG. 48. Histological changes of the lesion on the prepuce of Rabbit 5. Zenker
fixation, stained by hematoxylin-eosin. Showing the marked hyperkeratosis andconsiderable mononuclear infiltration of the interpapillary spaces. X 75.
FIG. 49. Section of chancre on scrotal skin of Rabbit 25 (Nichols strain) 28
days after inoculation, showing typical interstitial and perivascular infiltration ofmononuclear cells, and almost normal epidermis. The same fixation and staining
as Fig. 48, shown for comparison. × 75.

T H E JOURNAL OF E X P E R I M E N T A L M E D I C I N E VOL. X X X V .

PLATE 17.

(Noguchi: Venereal spirochetosis in American rabbits.)

T H E JOURNAL OF EXPERI M E N T A L M E D I C I N E VOL. X X X V .

PLATE 18.

(Noguchi: Venereal spirochetosis in American rabbits.)

THE JOURNAL OF E X P E R I M E N T A L ,',/IEDICINE VOL. X X X V .

PLATE 19.

(Noguchi: Venereal splrochetosis in American rabbits.)

THE JOURNAL OF E X P E R I M E N T A L M E D I C I N E V O L . X X X V .

PLATE 20.

(Noguchi: Venereal spirochetosis in American rabbits.)