ii2 SCIENCE PROGRESS. 



It is an old observation that the plague which is at first 

 a disease of rats and mice soon becomes a disease of man, and 

 all recent authors confirm this fact. That these animals are 

 really plague-stricken admits of no doubt. In Formosa 

 plague is known as rat-pest, and in Canton one man a'one 

 collected 22,000 dead rats during the outbreak in 1894. 

 Animals, as laboratory experiments prove, may succumb 

 either by ingestion of pieces of infective organs or by inocu- 

 lation at the surface of the body. When passed through a 

 series of animals the microbe, which on cultivation outside 

 the body is easily attentuated, acquires increased virulence, 

 in this respect resembling other bacteria such as those of 

 anthrax and chicken-cholera. H. F. Nuttall (20) has 

 shown that outbreaks of plague in various countries have 

 been described as preceded by or associated with the 

 death of various animals besides rats and mice. Not 

 only these, but also pigs, cats, dogs, snakes, horses, 

 buffaloes, goats, fowls and other birds have been stated 

 to be affected. Experiments conducted by Nuttall (20), 

 Yersin, Wilm, Galeotti and Malenchini (21), Lowson 

 and Devell (22) at the same time restrict and add to our 

 knowledge of the susceptibility of different animals, which 

 after subcutaneous inoculation, die in a few days with 

 symptoms of septicemic poisoning accompanied by a strong 

 reaction at the seat of the injection. Bubonic swellings of 

 the glands may or may not be present. According to 

 Nuttall's tables the following animals are susceptible : rats, 

 white mice, house mice, shrew mice, guinea-pigs, rabbits, 

 pigs, horses, monkeys, cats, fowls and lizards ; while 

 pigeons, dogs, oxen, the tortoise and frogs are immune. 

 One species of the latter (Rana temporaria) is stated by 

 Devell (22) to die of plague if bacterial cultures or pieces of 

 infected organs are introduced into the lymph sac of the 

 animal. A microbe of virulence sufficient to kill mice in 

 two to two and a half days requires thirteen to seventeen days 

 for a frog, but by passage through this animal the virulence 

 of the bacillus is augmented and the time so shortened that 

 death follows inoculation on the fifth day. Many animals 

 which under normal circumstances are immune to bacterial in- 



