Preventive Measures 309 



Yellow fever is kept out of the Canal Zone and 

 the cities of Panama and Colon by the following 

 measures: Inspection of arrivals, quarantine sus- 

 pects, and of all who have been less than six days 

 in transit from ports where yellow fever is present, 

 in order to complete the period of incubation of 

 yellow fever under observation. For quarantine 

 purposes this period is considered to be six days. 

 In the ports of Panama-Balboa and Colon-Cristobal 

 the quarantine officers board all vessels, and in 

 addition to the usual examination and quarantine 

 measures, detain those who appear at all likely to 

 be suffering from yellow fever, and also all those 

 who have boarded the ship at yellow fever ports 

 less than six days from the day of the inspection. 



The careful exercise of quarantine regulations 

 by vigilant, conscientious, and competent ofScers 

 makes it unlikely that a case of yellow fever can 

 land in a port, and be allowed to go at large. 



The three weak links in the chain are: 



1. An unrecognized case, in the early stages, 

 might be allowed to go at large. 



2. A person in the early stages of yellow fever 

 might land on the coast from some small vessel, 

 and find his way overland into the Canal Zone, 

 Panama, or Colon. This is possible, but ex- 

 tremely improbable because it would be a mat- 



