STUDIES ON PNEUMONIC PLAGUE AND PLAGUE 

 IMMUNIZATION. 



XI. THE INFECTION OF GUINEA PIGS, MONKEYS, AND RATS 



WITH DOSES OF PLAGUE BACILLI, RANGING 



FROM ONE BACILLUS UPWARDS. 



By M. A. Barber. 



(From the Biological Laboratory, Bureau of Science, Manila, P. I.) 



The method of isolation and inoculation of minute doses of 

 bacilli has been described in various papers^ by the writer and 

 needs but a short description here. 



The organisms to be manipulated are suspended in hanging 

 drops of liquid under a large cover glass. This cover is placed 

 over a moist chamber consisting of a glass box open at one end, 

 and the whole is mounted on the stage of the microscope. A 

 glass pipette, the end of which is drawn into a microscopically 

 fine capillary point, is attached to a special holder clamped to 

 the stage of the microscope. The capillary point, bent upward 

 at right angles, is raised by the holder into the hanging drop 

 containing the bacilli, both bacilli and point being kept in view 

 in the field of the microscope. The bacilli enter the point by 

 capillarity and may then be discharged on a sterile part of the 

 cover, or on a new cover, by blowing through a rubber tube 

 attached to the outer end of the pipette. Doses thus isolated are 

 taken up by a new sterile pipette and inoculated. The point is 

 made to pierce the skin of the animal, and the dose is injected by 

 blowing into the rubber tube attached to the pipette. Enough 

 salt solution is drawn into the inoculation-pipette before taking 

 up the dose to wash out the bacilli during the discharge, and 

 just before inoculation, enough sterile salt solution is drawn in 

 to wash the bacteria some distance back from the tip. This 

 is done to prevent the loss of the dose by the breaking off of 



'Sci. Bull., Kansas Univ. (1907), 4, 3. Journ. Infect. Dis. (1907), 5, 

 380; (1906), 6, 634; (1911), 8, 348. 



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