IMMUNITY AND IMMUNIZATION 311 



Pathogenesis. Animal. Apes are susceptible to Micrococcus meli- 

 tensis; the subcutaneous inoculation of cultures of the organism 

 leads to definite clinical symptoms parallel to those observed in 

 man. The disease usually runs a prolonged course and is often fatal. 

 Monkeys are somewhat less favorable subjects, than apes. (Goats, 

 sheep, cattle, and horses are also susceptible to infection, although 

 the disease is rarely generalized; the presence of the virus in the urine 

 of the males, the milk and urine of the females of these species is the 

 principal indication of infection.) The incubation period is from 

 five to fourteen days. Eyre 1 states that rabbits and guinea-pigs may 

 be infected, but not rats and mice. 



FIG. 43. Micrococcus melitensis and staphylococcus. X 1000. (Kolle and Hetsch.) 



Milk appears to be the chief source of infection; on the Island of 

 Malta, where Malta fever was first described, fully 10 per cent, of 

 the female goats contained the organism in their milk. Monkeys 

 readily contracted the disease by drinking this milk. The urine of 

 both male and female goats was shown to be infected as well. 



Immunity and Immunization. The blood and urine of infected indi- 

 viduals contain the virus of the disease and specific agglutinins are 

 present in the blood even early in the disease. The agglutinins may 

 persist for years after convalescence. Dilutions of ^ to 10 u UO 

 are made from the blood serum with suitable controls. A small amount 

 of growth from a three-day agar culture of the organism is thoroughly 

 emulsified in each dilution of serum and in the controls; the emulsions 

 are incubated at 37 C. for two hours, then placed in the ice-box for 

 twenty-four hours before the readings are made. A control with a 



1 Kolle u. Wasserman, Handh. d. Path. Mikroorganismen, I. Erganzband. 



