Page:Transactions of the Royal Society of Tropical Medicine and Hygiene, volume 1.djvu/90

 made discoveries in tropical medicine. Dr. von Prowazek showed us newly-discovered protozoa in trachoma from Sumatra, and Herr Giemsa, the chemist, explained to us by diagrams, the Nocht-Gieinsa apparatus for killing rats on ships. The gas derived from combustion of coke requires twelve hours to disinfect a large passenger steamer. We saw some rats killed with this gas in half a minute in a bell glass, and it is believed that all rats are destroyed on a steamer in about ten minutes after exposure to the gas. The gas consists of about 8 per cent, carbon monoxide, with a little carbonic acid, and some 70 per cent, of nitrogen.

The cost of disinfecting a moderate-sized steamer is £7 10s. In addition to the compulsory destruction of rats on vessels arriving from a plague-infected port, owners often request that rats, when a nuisance on a ship, should be killed by this method. The Giemsa apparatus does no harm to any cargo, and has this great advantage over Clayton's sulphurous-acid process.

When a ship arrives from a plague-infected or suspected port the rats on board are examined, especially when it is reported or discovered that any have been found dead or dying. For this purpose sample rats are sent to the Hygiene Institute, of which Professor Dunbar is the Director. If the jpost-niort&m examination of the rat shows plague or anything suspiciously like it, all the rats on board that steamer are destroyed before the cargo is landed. The crew are disembarked in a special place before fumigation begins, and are not allowed to return to the ship until the air has been tested by animals in cages to make certain that no dangerous gas-poisoning remains. The Nocht-Giemsa apparatus introduces gas into the hold and on completion of the process exhausts it again. Though the gas kills rats successfully, it does not disinfect the cargo, which must therefore be carefully removed by