252 



BARBER. 



the more delicate part of the tip during inoculation. That the 

 bacteria pass into the animal with the inoculating fluid and do 

 not remain behind in the pipette has been shown by a series of 

 controls where organisms were discharged into a suitable culture- 

 medium instead of into the animal. 



Most of the inoculations were made with a virulent strain 

 of plague which has been fatal to guinea pigs usually in three 

 to five days after cutaneous inoculaton. In the series "Shanghai," 

 a strain of somewhat less virulence was used. 



Bacilli were taken immediately from the blood or spleen of 

 infected animals or from the first cultures made from these 

 sources. In most cases bacilli from the heart's blood or organs 

 were grown for a few hours in hanging drop or test-tube in a 

 mixture of body fluid and water of condensation of ordinary 

 agar. When the formation of chains showed that the organisms 

 were multiplying, they were isolated and inoculated at once. 



Doses of 50 or less were carefully counted and larger doses 

 were counted or closely estimated; but in the summary given 

 here all doses are arranged in convenient groups. The doses 

 of one-half and three-fourths million were estimated by the 

 Thoma Zeiss counter. In the column giving the dosage, a pair 

 of very short elements clinging closely together were, in some 

 cases, reckoned as a single bacillus; though probably each ele- 

 ment was capable of individual growth. 



All animals were inoculated subcutaneously, the guinea pigs 

 and monkeys under the skin of the abdomen, the rats at the root 

 of the tail. 



Table I. — Guinea pigs mid virulent plague. 



Dose in number of bacilli. 



Number 

 of animals 

 inocu- 

 lated. 



Result. 



Infected 

 and died. 



Infected 



and 

 recovered. 



Not 

 infected. 



1 



Average 

 number 

 of days 

 between 

 inocula- 

 tion and 

 death. 



1 - 



9 



7 

 14 

 1 

 3 

 2 

 1 

 4 

 16 



6 

 3 



10 

 1 

 2 

 2 

 1 

 4 



16 





 

 

 

 1 

 

 

 

 



3 



4 

 4 

 

 

 

 

 

 



9.7 

 9.0 

 8.6 

 7.0 

 9.0 

 9.0 

 12.0 

 6.5 

 4.8 



2 to 10 



11 to 50 - - 



51 to 100 



101 to 200 



201 to 500 . 



2.000 - 





f million 



Total number receiving doses of 1 to 500, 36. Per cent of fatal infections, 63.9. 



