PATHOGENICITY FOR EXPERIMENTAL ANIMALS 185 



In an investigation of the physiological variables responsible for 

 the lack of uniformity in the behavior of rabbits to intradermal 

 inoculation with Pneumococcus, Goodner 532 concluded that, since 

 normal rabbits lacked any form of specific antipneumococcal anti- 

 bodies, resistance to intradermal inoculation in combination with 

 passive immunization with specific immune serum was determined 

 by the physiological condition favorable to the utilization of pas- 

 sively conferred specific antibodies, which in turn depended upon 

 the weight and white blood-cell count of the rabbits. Animals, 

 therefore, that are physiologically mature possess an advantage 

 over animals less mature and with a lower cell activity. 



Another factor affecting the resistance of rabbits to infection is 

 vitamin deficiency. Greene 554 reported that rachitic rabbits showed 

 a greater morbidity and mortality from intranasal inoculation 

 with Type I Pneumococcus than did normal controls. Differences 

 in the susceptibility of rabbits of diverse breeds has also been 

 noted ; hence, in the selection of rabbits for comparative or quanti- 

 tative tests on the virulence of strains or types of pneumococci or 

 for measuring the potency of immune serum, consideration should 

 be given to the breed, age, weight, and diet of the test animals. 



THE GUINEA PIG 



The comparatively low and variable susceptibility of guinea 

 pigs precludes their use for many purposes in experimental studies 

 on Pneumococcus. The susceptibility of the guinea pig to pneumo- 

 cocci administered by inhalation was first demonstrated by Neu- 

 feld and Ungermann 10012 in 1912. The inoculation, in some cases 

 but not regularly, produced a slow pneumonic process. When the 

 culture was injected directly into the lung, the animals developed 

 acute infection, dying in one or two days from pleuropneumonia or 

 bronchopneumonia. 



The intrapleural injection of pneumococci into guinea pigs may 

 cause a pleuropneumonia, as shown by Kolmer. 741 Neufeld and 

 Ungermann 1001 " 2 and also Engwer 365 reported similar successful in- 



