Sectiou G. 



14 



These restrictions, especially the last, have by no means been absolute 

 for all classes of vessels, but are well observed, in Cuban and Mexican 

 ports at least, by probably over five-sixths of the tonnage. The sani- 

 tary measures to avoid infection (3) and the proportionate substitution 

 of foreign sailing vessels by steamships (2) are without doubt the main 

 factors acting in cooperation in lessening the infection of ships. No 

 one can read Burgess' list of infected vessels in Havana Harbor (Eeport, 

 U. S. Marine-Hospital Service, 1896) without noting how great has been 

 that decrease in recent years. 



We have said that if a case of yellow fever develops aboard a vessel 

 harboring the stegomyia mosquito (proper conditions of temperature 

 being premised) that they may become contaminated by feeding on him 

 and infect others. A vessel which has no stegomyia aboard is like 

 ''noninfectible territory" and will not communicate infection, even if 

 cases of yellow fever develop aboard. I think it fair to say that ves- 

 sels plying to and from southern ports of the United States will, during 

 the summer season, generally have the stegomyia aboard, independently 

 of its berth in tropical harbors, and may at times breed them in their 

 water supply. This mosquito, however, seems to be rare north of Vir- 

 ginia Beach (its distribution has not been sufficiently investigated, 

 however), and a vessel plying to and from a northern port of the United 

 States would not harbor this mosquito unless it came aboard in the 

 tropical port. Now how far this mosquito goes or is borne from shore 

 has not, I think, been directly investigated, but we do know that the 

 crews of vessels moored off from shore (say 200 or more fathoms) in 

 that part of Havana harbor seaward from the line between the Sta. 

 Catalina warehouses and the Machina wharf do not develop yellow 

 fever (unless close to some vessel which is infected). This means that 

 contaminated stegomyia, at least, do not go so far from shore. Lying 

 then at the anchorages accounted safe in Havana harbor, where the 

 passenger vessels for the United States lie, one would think that the 

 probability of any stegomyia coming aboard would be small. At Vera 

 Cruz the vessels must lie nearer shore (although to windward of it), 

 and experience shows that the crews of vessels lying there are not entirely 

 safe, as I believe them to be in Havana, although infection in the part of 

 the harbor picked out as safe is decidedly rare. The anchorages in both 

 harbors regarded as safe are well to the windward of the town all sum- 

 mer. A direct investigation of this matter — i. e., the presence of the 

 stegomyia aboard vessels from northern ports in different parts of the 

 harbor of Havana and other tropical harbors, should be made. 



To sum up^- 



1. Vessels aboard which yellow fever had been contracted — i. e., 

 vessels infected with yellow fever have not been rare, at least at south- 

 ern quarantine stations. 



2. Such vessels are much rarer since 1893, and are not very common 

 now. 



