Sanitation 



597 



caution should be taken to prevent the entrance of rats, first by 

 anchoring in the stream instead of tying to the dock; by carefully 

 scrutinizing the packages taken from the lighters to see that there 

 are no rats hidden among them; by placing large metal shields or 

 reversed funnels about all anchor chains, hawsers, and cables so 

 that no rats can cUmb up from the water in which they are swim- 

 ming at night. Arrangements should also be made for rat destruc- 

 tion on board the ship by means of sulphurous oxid or other poi- 

 sonous vapors to rid the ship of rats before the next port is reached. 



Fig. 237. — Healthy rat to be contrasted with plague-infected rat, Fig. 236. 



Passengers and crew should also be kept in quarantine before ming- 

 ling with society. It is much more easy to keep plague out of a 

 port than to combat it when it has entered, for under the latter 

 condition are involved the isolation of the patients in rat-free and 

 vermin-free quarters, the disinfection of the premises and goods 

 where the case arose, and an immediate warfare upon the rats and 

 other small animals of the neighborhood. To emphasize how 

 difficult the latter may be it is only necessary to point out that 

 plague reached San Francisco in May, 1907, during which year 



