BACILLUS PESTIS 135 



minutes. They resist drying for two or three days 

 under natural conditions, but when drying is hastened 

 by artificial means, they live only a few hours. They 

 resist cold and freezing for a long time, perhaps a 

 month. Sunlight destroys them in five hours. In 

 pus or sputum the}' may live a few weeks, but in 

 cadavers they have been found after several months. 

 Chemicals kill them as follows: 5 per cent, carbolic 

 acid and 1 to 1000 bichloride in ten minutes. Animals 

 are usually susceptible to Bacillus pestis, particularly 

 guinea-pigs and rats, and it is said that simple rubbing 

 of the germs on the skin of these beasts will produce the 

 infection. It is similar to the human disease. 



Plague Serum. The poison of Bacillus pestis is 

 largely intracellular. It has been possible to get an 

 antiserum from horses which will destroy the bacteria 

 and can be used therapeutically. The bacteria grown 

 in the laboratory are killed by moderate heat and 

 injected into animals. The injections are continued 

 until very large doses, fatal to unprepared animals, are 

 withstood. The serum now has properties which will 

 neutralize the endotoxins of the plague bacillus, and 

 is called a bactericidal serum. It is said to have also 

 some antitoxic properties that neutralize the small 

 amount of extracellular poison of this organism. This 

 serum is used for treatment during the attack or for 

 immunizing those exposed. The serum is injected 

 under the skin for preventive purposes, but during an 

 attack it is well to give it into the circulation. 



Not only is this passive immunity made use of, but 

 for prevention of infection, plague bacilli whose patho- 

 genic properties are destroyed by heat are also injected 



