as Enemies of Mankind. 



17 



as biological and medical studies proceed. In this place we can 

 discuss only a few of them, but the few will suffice to prove that, 

 even in these days, humanity possesses no more deadly enemy 

 than the rat, and that the rat problem is as serious and urgent as 

 any before the public at present. Whatever the cost in labour or 

 money may be, the extermination of the rat is a necessary step for 

 the public safety. 



Plague. — The great tragedies wrought by this disease in 

 Western Europe, from early mediaeval times down to the begin- 

 ning of the last century, are famihar to all. Plague is by no 

 means extinct. During the last twenty years it has killed millions 

 of people in various parts of Asia ; from the East it has spread 

 and is still spreading to all quarters of the globe. It shows every- 

 where a virulence of type which augurs ill for Europeans should 

 they fail to keep the disease under control. In almost each of the 

 last ten years several deaths have occurred in Great Britain. 



Plague is a disease of the circulatory and respiratory systems 

 resulting from an invasion of the body by a minute organism, the 

 Bacillus pestis. The disease exists in two forms, viz., Bubonic 

 plague and Pneumonic plague ; these differ merely in their mode 

 of infection and symptomatically. In bubonic plague the blood is 

 infected ; typically, the bacilli are arrested in the glands, which 

 swell into buboes and suppurate. In more acute cases the glands 

 fail to arrest the bacilli, and the battle between the latter and the 

 phagocytes is fought out in the blood, giving rise to what is called 

 " septicaemic plague." In pneumonic plague the puhnonary 

 organs are infected with the bacilli, and the ensuing symptoms 

 closely resemble those of pneumonia. In either form the disease, 

 in the majority of cases, terminates fatally. 



This dreadful scourge belongs essentially to rats and the 

 peculiar species of fleas infesting them ; it is Nature's unfailing 

 method of periodically reducing the rat population to reasonable 

 proportions. The rat fleas feed on the blood of an infected rat ; 

 at one meal a single flea can take v/ith this blood as many as 

 5,000 plague germs into its stomach. Bacillus j^estis multiplies 

 in the stomach of the flea rapidly — so rapidly that an obstruction 

 is often formed in the alimentary canal of the flea near the 

 entrance to its stomach. Such a flea grows hungry, in due 

 course, and endeavours to feed ; but although it can still pump 

 blood from its host, the obstruction in its gullet prevents it from 

 swallowing, and so the blood is forced back into the wound ; the 



