to not less than 18 in. below the level of the ground floor, and that the latter should be made of concrete 3 in. thick, covered with J in. of cement. All ventilators should be protected with iron gratings, and all openings around wires and pipes cemented. The mooring cables of ships should be shielded in such a way as to prevent egress or ingress of rats, and all gangways should be taken up at night or when not in use.
Attempts have been made to set up an epidemic among the rats which should not be communicable to man. For this purpose the bacillus discovered by Danysz was recommended by him. But the method employed viz. inoculating a few rats with the bacillus and then allowing them to escape, in the hope that when they sickened they would be eaten by other rats, which would in their turn be taken ill, and an epidemic be thus set up has not been successful. Experiments on these lines have failed. The Danysz bacillus was, however, found to be useful in Cape Town and elsewhere for the destruction of rats when a system introduced by Professor Simpson was adopted, and bread soaked in the cultures was distributed and laid down in the same way as is usually done with biscuits on which rat poison is spread. By distributing thousands of doses an excellent result was obtained, and rats which were examined in the localities where the Danysz bacillus had been used in this way were found to have died from the disease induced by this organism. Rats which had migrated were also found to have died of the same cause in localities other than those in which the cultures were placed. An important point in the success attending these operations was found by Dr.R. W. Dodgson to be the raising and maintenance of the virulence of the cultures. Those sent out from the Pasteur laboratory after a fortnight's voyage were found to be useless, and consequently required to be exalted in virulence by a series of passages through healthy rats.*[1]
- ↑ * Danysz's bacillus rapidly loses its virulence when grown on the ordinary culture media, but retains it if grown on eggalbumin media, killing rats in from seven to nine days.
