432 BIOLOGY OF THE LABORATORY MOUSE 



lactating albino mice (149, 150), in the seminal vesicles* of t,^ of 34 male 

 mice, and in Bartholin (clitoral) glands* of 6 female mice (260), in the blood 

 of 15 of 31 apparently normal white mice (131), in 6 of 8 white mice of one 

 stock and 65 of 150 mice (two examinations) of a different stock (79). 

 Other investigations give the incidence as i to 4 per cent (338, 241). 



Mice infected spontaneously or experimentally usually remain healthy, 

 showing no signs of illness and only slight splenic enlargement if killed. 

 With repeated passage, however, the spirillum may become more virulent 

 and produce death in approximately 14 days (221). Organisms appear in 

 the blood 9 to 15 days after inoculation, gradually increase in number 

 for I or 2 weeks, then slowly decline (241, 267, 222). At the height of 

 the infection one or more spirilla may be found per microscopic field by 

 dark field examination. Rarely, they may be demonstrable as long as 

 II months after injection. The susceptibility of the mouse and the ease of 

 demonstrating the organisms would make this animal an ideal one for 

 diagnosis of the disease in other animals were it not for the above incidence 

 of natural infection. 



Transmission of infection in wild or stock animals presumably occurs by 

 biting and contamination of food and water with urine (241). Hereditary 

 transmission is both affirmed (11, 150) and denied (267). Infection of 

 suckling mice by ingestion of organisms in the milk (149, 150) and from 

 mouse to mouse by sexual contact (260) has been proposed. 



Spirillum minus is a rapidly motile, rigid organism, having from two to 

 six regular spirals. The ends taper and are provided with one or more 

 flagella. It is perhaps best observed by dark field examination, but it can 

 be stained by aniline dyes or by silver impregnation methods. The 

 organism probably should be classified as a bacterium in the same family 

 as the vibrio group, although common usage includes it with the 

 Spirachaeta. 



Various strains isolated from mice, rats, and cases of human infection 

 have been studied rather extensively in an attempt to differentiate them 

 (338, 223, 240, 241). Some differences in virulence and serological reac- 



* The identification of the spiral organisms found by Stroesco (260) in the seminal 

 vesicles and Bartholin's glands as Spirillum minus was based on morphological appear- 

 ance in stained sections of tissue. Dubois (59) has shown that this organism is more 

 like a spirochete in morphology and motility and further differs from S. minus in 

 pathogenicity and resistance to chemotherapeutic agents. Both Dubois and ISIack- 

 enzie (160) consider it to be a new, non-pathogenic species which must be differentiated 

 from 5. minus. 



