136 LABORATORY BACTERIOLOGY 



cases of mixed cultures taken directly from the suspected throat it 

 is desirable to inoculate one or more guinea pigs to determine 

 whether the suspected organism present is a virulent Klebs-LoeiHer 

 bacterium. In these cases a suspension of the growth on the serum 

 may be injected. The guinea pig dies usually in from 36 to 80 

 hours. The lesions produced have been described by Park as 

 follows,: 



" At the seat of inoculation there is a grayish focus surrounded by 

 an area of congestion ; the subcutaneous tissues for some distance 

 around are cedematous ; the adjacent lymph nodes are swollen ; and 

 the serous cavities, especially the pleural and the pericardial, fre- 

 quently contain an excess of fluid, usually clear, but at times turbid ; 

 the lungs are generally congested. In the organs are found numer- 

 ous smaller and larger masses of necrotic cells, which are permeated 

 by leucocytes. The heart and voluntary muscle fibres usually show 

 degenerative changes. Occasionally there is fatty degeneration of 

 the liver and kidneys. The number of leucocytes in the blood is 

 increased. From the area surrounding the point of inoculation, vir- 

 ulent bacilli may be obtained, but in the internal organs they are 

 only occasionally found, unless an enormous number of bacilli have 

 been injected. Paralysis, commencing usually in the posterior ex- 

 tremities, and then gradually extending to other portions of the body 

 and causing death by paralysis of the heart or respiratory organs, 

 is also produced in many cases in which the inoculated animals do 

 not succumb to a too rapid intoxication." 



Guinea pigs are used for testing the virulence of pure cultures and 

 the strength of the toxin and antitoxin. For further details, see 

 text-books of bacteriology. 



