458 Biology in America 



danger of an occasional recurrence of the disease among ns 

 becomes still greater. 



"Without the aid of biology we should still be living in the 

 Dark Ages so far as plague is concerned. With the discovery 

 of the bacillus causing the disease in 1894 it was shown that 

 mice, rats, guinea pigs, rabbits, monkeys and many otlicr 

 animals can be infected by inoculation as well as by feeding 

 with infected material. But how was the disease trans- 

 ferred from man to man? Was it a "miasma" or foul air 

 which did the damage? Was it by "fomites" or infected 

 clothing and other articles that contagion was spread? Or 

 was personal contact necessary for infection? Here enters 

 the ubiquitous flea. The Indian Plague Commission appointed 

 by the British Government to study the scourge in India 

 found that it was only in the presence of fleas that con- 

 tagion was spread from one animal to another. Young rats 

 may even be suckled by plague-infected mothers witliout con- 

 tracting^ the disease, provided fleas are absent from their 

 cages. Rats and guinea pigs may be kept healthy in cages 

 hung in rooms where animals have recently died of plague. 

 But if the cages be hung near enough to the floor to permit 

 the fleas to jump in, they become infected. On the other 

 hand the cages may be placed upon the floor without danger 

 of infection, provided only they be surrounded with "tangle 

 foot" thereby preventing ingress of fleas. Furthermore con- 

 tagion may be spread through the transfer of fleas from 

 infected to healthy animals without any contact between the 

 latter. In the light of these experiments proof appears to 

 be conclusive that the flea is the most important, if not the 

 only direct intermediary in the spread of plague. ^"'^ 



But the flea does not confine his attentions to rats alone. 

 He believes in a varied diet, and an occasional meal of human 

 blood is quite to his taste. Consequently in rat-infested and 

 dirty dwellings, where fleas abound, if plague breaks out 

 among the rats, their human co-habitants are almost certain 

 to be stricken likewise. 



Previous to 1900 plague had never occurred in the United 

 States although it had visited IMexico and South America. 

 In this year there was an outbreak of plague in ' ' Chinatown 

 in San Francisco, followed in 1907-8, a year after the great 

 earthquake and fire, by a second outbreak, in both of which 

 there was a total of 281 cases and 85 deatlis. When the 

 disease was discovered the city authorities at first adopted 

 the ostrich policy and endeavored to suppress all information 

 relative to it. 



"In San Francisco plague met politics. Instead of being 

 confronted by a united authority with intelligent plans Jor 



"* Pneumonic plague niay be transmitted direct by the breath. 



