246 BARBER. 



from 0.25 to 6 cubic centimeters, were inoculated both subcu- 

 taneously and intraperitoneally by means of an ordinary syringe. 

 Especial precautions were taken against contamination; for a 

 contaminating organism might develop rapidly under protec- 

 tion of the agar. The escape of the still liquid agar could be 

 prevented by applying ice or cold water to the point of inocula- 

 tion after withdrawing the needle. 



It was found that if the agar mass was deposited immediately 

 under the skin, necrosis of the overlying skin sometimes oc- 

 curred. This could be avoided by depositing the agar well into 

 the subcutaneous tissues. Few cases of death due to a contami- 

 nating organism Occurred. 



In order to observe the behavior of the inoculations, animals, 

 some of them inoculated with agar alone and some with the 

 agar pest mixture, were sacrificed at the following periods after 

 inoculation: three and one-half hours, twenty-one hours, forty- 

 eight hours, three days, four days, five days, six days, seven 

 days, twenty-one days, and twenty-nine days. In all cases the 

 agar mass with the surrounding tissues was studied in frozen 

 sections. 



The agar mass examined soon after inoculation was found to 

 be permeated by connective tissue fibers more or less stretched 

 by the agar. Within a few hours leucocytes begin to invade 

 the mass, following the larger strands of connective tissue. They 

 become more and more abundant as time goes on, and within 

 two or three days part of the mass may become semifluid. This 

 was more marked in the agar and pest inoculations. Areas of 

 agar could be detected up to the twenty-ninth day, at least. 

 Colonies of plague, some of them 30 iip, in diameter, were found 

 scattered in the agar mass as early as twenty-one hours after 

 inoculation and as late as five days. As the time went on the 

 agar became more and more invaded by leucocytes and the zone 

 of granulation tissue encroached more and more on the agar, 

 until nothing but a small hard lump of scar tissue could be felt. 

 In some cases this lump could be felt as late as two months after 

 inoculation. In a few cases a softer abscess persisted many 

 weeks. 



The contents of the agar mass was examined for plague bacilli 

 in all sacrificed animals and in some living animals by withdraw- 

 ing some of the mass by means of a glass capillary pipette. 

 Living plague bacilli were detected in practically all sacrificed 



