PART ONE 



INTRODUCTION 



Then said they, What shall be the trespass offering which we 

 shall return to him? They answered, five golden emerods, 

 and five golden mice, according to the number of the 

 lords of the Philistines : for one plague was on you all and 

 on your lords. 



I Samuel 6 



THE CHILDREN OF ISRAEL kncw that the bubonic plague was intimately 

 connected with rats. Indeed, a profound and intensive study of the 

 Bible might well have prevented, or at any rate reduced, the ravages 

 of the Great Plague of London. There is no hint, however, that the 

 ancient Hebrews were aware of the sinister role played by the rat 

 fleas, which, by their promiscuous feeding habits, spread the plague 

 bacillus from rodent to rodent and from rodent to man. The writers of 

 the Old Testament concentrated on essentials and, in this case, were 

 entirely justified in focusing their attention on the rats and mice them- 

 selves, for they are the true hosts of the bacillus in question. 



To-day, in studying bubonic plague a large section of parasitology 

 and many of its related problems must be considered. A detailed 

 knowledge of the parasitic bacteria which cause the Black Death in 

 rats and, secondarily in man, is, of course involved, but it is also 

 necessary to study associated animals such as fleas, which act as carriers 

 and spread the disease, as well as a whole series of complex factors, 

 like climate, food and the habits and behaviour of the living organisms 

 involved. At one end of the chain we are concerned with the minute 

 differences in the sex organs of fleas and at the other with the inter- 

 national grain commerce of man. 



