Exposure of the bacillus in thin layers to the direct action of sunlight destroys it after from three to four hours, but to accomplish a like result from exposure to diffuse light as many days are necessary. The germ is killed by an exposure to a temperature of 80° C. for thirty minutes and at 100° C. within a few minutes. Spore formation has not been observed.
There is some reason for believing that there is a pseudo-bacillus of the plague as there is one of diphtheria. In his studies of the soil of the infected districts of Hong Kong, Yersin found a bacillus that resembled that obtained from persons with the disease, both morphologically and in its growth on culture media, but it was without effect upon mice and guinea pigs. He also observed great differences in virulence in the germs obtained from the sick; some of these were without effect upon the above-mentioned animals. There were, moreover, observable variations in the size of the bacilli found in the bodies of the sick and dead.
The studies of Yersin and Kitasato were interrupted by the war between China and Japan, and a much more thorough knowledge of the bacillus and the disease caused by it will probably soon be in our possession.
I will now consider some of the characteristic symptoms of the disease. It is undoubtedly a septicemia, or form of blood-poisoning. As has been stated, the bacillus is found in the blood and in all the organs. It is customary to describe the disease under two forms. The milder epidemics are known under the name of pestis minor. In this form the glands of the groins and armpits swell and either suppurate or undergo resolution. There is moderate fever, although in exceptional cases the temperature may reach 104° F. The disease usually continues from ten to twenty days, and may last for from four to eight weeks. Pestis minor sometimes precedes and at other times follows the more severe forms of the disease. The former was the case in the epidemics in Mesopotamia in 1873 to 1878, and in Astrakhan in 1878.
Foderé, as quoted by Cantline, makes the following statement concerning pestis minor: "In the Levant and in the Marseilles epidemics of 1820, cases were to be seen which were not ushered in by any alarming symptoms, and where the natural functions were undisturbed, and where buboes and carbuncles appeared without fever, or only with slight fever, or the buboes went on to a healthy suppuration more or less prompt, or even disappeared and went on to resolution without the help of art, without any inconvenience, and with a perfect integrity of all the functions. This state is comparable to benign smallpox, during which children play together and walk in the streets without any precautions, no care
