266 MANUAL OF BACTERIOLOGY. 



On agar containing 3 per cent, of common salt remark- 

 able involution forms appear. The stalactite growths and 

 the forms occurring on salt-agar are considered the most 

 characteristic cultural tests. 1 



It is sometimes sensitive to drying, but may survive pro- 

 longed drying. It is killed in three to four hours by direct 

 sunlight, when spread in thin layers; in a few minutes by 

 steam at 100 C., and in one hour by I per cent, carbolic 

 acid. 2 It is pathogenic to rats, mice, guinea-pigs, rabbits, 

 and a number of other animals. 



In man it appears usually to enter through wounds of 

 the skin. Other possible avenues of infection are the air 

 passages, the mouth, and the gastrointestinal tract. Plague 

 is usually regarded as having three different possible forms, 

 the bubonic, the pneumonic and the septicemic. The 

 bubonic form is commonest. The point in the skin at which 

 the inoculation takes place seems generally to exhibit no 

 inflammatory reaction. The lymph-nodes are generally 

 swollen, especially the deep inguinal and axillary nodes. 

 The swollen lymph-nodes may suppurate. The suppurating 

 nodes often are infected simultaneously with micrococci. 

 The bacilli are numerous in the enlarged lymph-nodes, but 

 may be detected in the other organs of the body and in the 

 blood. Fluid drawn from the buboes with a hypodermic 

 needle may be examined microscopically, by cultures and by 

 inoculation into rats or guinea-pigs. In the pneumonic or 

 pulmonary form the bacilli occur in the sputum, and may 

 be tested in the same manner. This type of the disease is 

 said to be very fatal. In the septicemic form no primary 

 bubo is found, or a bubonic case may become septicemic. 

 This form is very fatal. 



1 Wilson, Journal Medical Research, Vol. VI., 1901. 



2 See Viability of Bacillus pestis, Rosenau, Marine Hospital Service, 

 Hygienic Lab'y, Bull. No. 4, 1901. 



