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by means of which the gas is delivered to the various holds and 

 compartments of the vessel. To be at all effective the gas must be 

 4J per cent strength, with at least twenty-four hours exposure. The 

 one recommendation of such a system is its freedom from danger by 

 fire. It is too slow; the pipes, even where 6 inches in diameter, are 

 liable to clogging with sublimed sulphur, an inevitable result if the 

 fans are driven too rapidly, and it is not possible to do more than 

 one or at most two ships at a time. The inadequacy of such a 

 method when compared to the work done in San Francisco where we 

 averaged over nine vessels every day for almost fourteen months is 

 at once apparent. Many ships now carry their own disinfecting 

 plants, by means of which not only is sulphur dioxide generated and 

 pumped into a compartment, but at the same time also the air of 

 this space is sucked out. This principle is excellent, but in its appli- 

 cation the machines used are wholly inadequate, having a very lim- 

 ited sulphur capacity per hour and equipped with delivery pipes in 

 many instances only 2 or 3 inches in diameter. It would be a matter 

 of days to disinfect some of these ships with the machines they carry. 

 In San Francisco we again and again used pots and pans to fumigate 

 these vessels, including the very compartments in which their own 

 machines sat doing nothing. 



The Marot system of generating the gas from compressed liquid 

 sulphur dioxide has in this country been found too expensive to 

 apply to vessels. Probably no system will effectually destroy all the 

 rats on a cargo-laden vessel. 



SUMMARY. 

 To summarize then: 



1. The rat is found on all vessels, sometimes in enormous numbers, 

 and is able to adapt himself to all sorts of conditions. He either 

 gets on board himself or is carried on in cargo. Owing to his sea- 

 going tendency, his distribution is world-wide. 



2. On shipboard, to live he must do damage to either cargo or 

 stores, or both. 



3. Plague is primarily a rat disease; it may exist in the rat in a 

 chronic form. Hence where ships go plague will go sooner or later. 



4. To prevent the ingress of rats and the consequent spread of 

 plague, ships should observe antirat precautions, and cargo inspec- 

 tion should be included in these. 



5. At stated intervals, three or, better still, four times a year, all 

 vessels should be fumigated for the destruction of rats. 



6. On empty vessels this can best be done by generating sulphur 

 by the pot and pan method. 



7. On laden vessels some special apparatus must be used to gen- 

 erate the gas. A longer exposure is required, at least twenty-four 

 hours, and the gas should be 4i per cent strength instead of 3 per- 

 cent. ' It is extremely difficult by any method to kill all the rats on 



a cargo-laden vessel. 

 13429—10 15 



