PATHOGENICITY OF TREPONEMA PALLIDUM FOR ANIMALS 917 



syphilitic rabbit's cornea into the anterior chamber of the eye of a fresh rabbit is followed 

 by complete heaUng of the local wound in 5 to 10 days. After 3 to 6 weeks, as a rule, 

 pericorneal congestion commences, followed by pannus and keratitis. The keratitis 

 increases to an acme, after which retrogression and healing occur ; this process may take 

 weeks or months to complete, and may be interrupted by a relapse. Only a certain pro- 

 portion of rabbits develop keratitis. The lesion is very much easier to produce by inocula- 

 tion of rabbit than of human syphilitic material. Successive passages of the virus through 

 the eye of rabbits resulted in an increase of virulence, manifested by a reduction in the 

 incubation period from 6 to 8 weeks to 4 to 5 weeks. 



Syphilis may also be conveyed to rabbits by inoculation into the testicle ; this method 

 of transference was first successfully used by Parodi(1907). As with ocular injection, the 

 implantation of human syphilitic material gives much less constant results than of that from 

 the rabbit. Uhlenhuth and Mulzer (1913), for example, inoculated 27 rabbits intratesti- 

 cularly with human syphilitic material — the juice from primary chancres — and obtained 

 only 5 positive reactions. But after 15 passages through the rabbit the virulence had so 

 increased that inoculation was almost uniformly successful, and the severity and extent 

 of the disease were correspondmgly greater. Brown and Pearce (1920a), using the method 

 of intratesticular inoculation of ground-up syphilitic rabbit's testicle suspended in saline, 

 were likewise uniformly successful in producing the disease. After an incubation period 

 of about 3 to 4 weeks the testicle commences to swell, and soon reaches the size of a pigeon's 

 egg ; the inflammation also affects the epididymis and cord. Sometimes a small superficial 

 erosion may develop at the site of inoculation, covered with a dry yellowish- brown adhesive 

 crust; or an actual chancre may appear. According to Brown and Pearce (1920a) the 

 testicular reaction pursues a cyclic or relapsing course, periods of active progression alter- 

 nating with periods of quiescence or retrogression ; these phases apparently correspond with 

 the variations in the number of spirochsetes in the lesion. The length of time that the testicle 

 is inflamed varies ; the lesion may disappear in 6 weeks, or it may last for over a year. 



The method of intracutaneous or subcutaneous injection of rabbit syphilitic material 

 into the scrotum, introduced by Tomasczewski (1910), gives rise after an incubation period 

 of about a fortnight to a typical primary chancre with a central necrotic area and indurated 

 edges. Sometimes a diffuse lesion of the scrotum follows. These scrotal lesions are invari- 

 ably accompanied by marked inguinal lymphadenitis. The scrotal infection may spread, 

 and numerous secondary lesions develop, lasting from 1 to 18 months. 



Following on scrotal or testicular infection, generalized lesions may develop afifecting 

 practically any structure of the body (Brown and Pearce 19206, 1921a, Brown et al. 1921). 

 Thus there may be : papular or erythematous eruptions on the skin, sometimes appearing 

 in successive crops ; granulomatous lesions of the skin passing on to ulceration ; alopecia, 

 onychia, and paronychia ; necrotic and ulcerative lesions of the mucosae and muco- 

 cutaneous borders ; localized lesions of the periosteum, bone, cartilage, tendons, and tendon 

 sheaths, including such typical manifestations as destruction of the nasal septum and 

 separation of the epiphyses ; conjunctivitis, keratitis, and iritis. Generalized lesions of 

 syphilis may also be produced by the intravenous or intracardial injection of rabbits a 

 few days old (Uhlenhuth and Mulzer 1913). For discussion of immunity in rabbits see 

 p. 1165, Chapter 51. 



Monkeys. — The experiments of MetchnikofF and Roux (1903, 1904a, b, 1905) amplified 

 the earlier observations of Klebs in 1875-77 (see Klebs 1932), and showed that syphilis 

 might be transmitted to the anthropoid apes, and with less certainty to monkeys. Of 

 the apes the chimpanzee appeared to be the most susceptible. Altogether they inoculated 

 22 chimpanzees {Troglodytes niger and T. cnlviis) with syphilitic material, either of human 

 origin or derived from experimental animals, and succeeded in producing disease in all 

 of them. Inoculation was performed by scarification of the genitals, the thigh, or 

 the eyebrow. After an incubation period of 15 to 49 days, generally 4 weeks, a primary 

 chancre developed at the site of inoculation, and was followed in a few days by swelling 

 of the focal lymph glands. Many of the animals developed lesions of secondary syphilis 



