26l 



by the bite affords entrant e to plague bacilli when the bodies of the 



inched <r when ihc inh re intn.diKed by the 



rubbing >r scratching of tin- wound. 



The 3pedefl Of rat llea most common in ihc orient b thecosmo- 



poli tan "plague flea," .\V;/f>/>.vy/A/ <l/n>/)is. 



In tlu- I'nited States the most common rat flea i\ ( Vr////;/>//\7//f.s 

 iiiscitiliis. The common cat and dog llea. Clcno<c()h>ilus nmi 

 ratS ad docs the human lira, I'ulcx irritnus; and all tlior .-pe< ies are 

 known to bite man. 



Plague in San Francisco. Plague, long dreaded in Ameri<an sea- 

 ports, finally entered San I-'rancisco in 1900, killed 114 persons in the 

 next four years, became dormant and broke forth again, with violence, 

 in 1007. The city, just beginning to recover from the great fire of the 

 year before, was in a frightful sanitary condition and most of the popu- 

 lation, engage* 1 in the work of reconstruction, paid little attention to 

 the deaths from plague and at first gave little aid toward the suppression 

 of the disease. As may be imagined, the campaign against the dis- 

 ease undertaken by the U. S. Public Health and Marine-Hospital 

 Service was carried on in the face of great odds. It was, however, con- 

 ducted most efficiently and successfully under the command of Dr. 

 Rupert Blue (later Surgeon- General), who wisely attacked the disease 

 by attacking the rat population. 



The labor involved in starving out the rats, trapping or poisoning 

 them, and making buildings rat-proof by the use of concrete or sheet 

 iron, was immense; but the undertaking was nevertheless carried to a 

 successful conclusion. More than one million rats were killed and the 

 disease was checked. 



In California plague affects ground squirrels, which doubtless con- 

 tract the disease from the rats that use the runways of the squirrels in 

 the fields. 



TRYPANOSOMIASES 



Some of the diseases known as trypanosomiases are among the dead- 

 liest that affect man and other vertebrates, and pathogenic trypano- 

 somes the organisms causing these diseases have received an 

 immense amount of study during recent years. 



Trypanosomes. The organisms under consideration are flagellate 

 protozoans. A typical trypanosome, for example, T. lewisi (Fig. 274) 

 of the rat, is essentially an elongated cell, tapering at each end, serpe.ii- 



