128 



among them) it is possible that the flea may be driven by hunger to- 

 attack man. The author has tried to ascertain whether fleas deprived 

 of their food under such circumstances are sufficiently numerous to be 

 likely to infect man with bubonic plague. Two experiments are 

 described. It would appear that when rats are not constantly in the 

 immediate neighbourhood of fleas owing to their scarcity, the total loss 

 of fleas is considerably greater (38-43 per cent, of the total number) 

 than when the host is constantly present. This fact must be considered 

 when investigating the possibility of man being infected with bubonic 

 plague by living rats which have only been temporarily in his vicinity. 



De Eaadt (0. L. E.). Bijdrage tot de Kennis der epidemiologic van 

 de pest op Java. [Contribution to the knowledge of the epidemi- 

 ology of plague in Java.] — Meded. Burgerh'jk. Geneesk. Dienst 

 Ned.-Indie, Batavia, 1915, pt. 4, 1916, pp. 20-38, 3 plates. 



The first part of this paper deals with researches in connection with 

 the significance of the rat-fleas found on Javanese rats for determining 

 the source of these rats. It would appear that Xenopsylla cheopis- 

 is most prevalent on rats caught indoors, much less so on rats caught 

 in the fields, and that it is entirely absent on rats taken from the cofiee 

 plantations, while Pygiopsylla ahalae is most prevalent on rats from 

 the coffee plantations, much less so on those from houses and least of 

 all on those from the fields. The conclusion drawn from this is that the 

 necessary conditions for the development of X. cheopis are solely to be 

 found indoors and this flea may therefore, to a certain extent, be called 

 a house flea. Its appearance on rats taken in the fields and in coffea 

 plantations can only be explained by its transportation from the 

 houses by means of house- and also of field-rats. It is further held 

 that the conditions for the development of Pygiopsylla ahalae are most 

 favourable in the coffee plantations and probably also in the woods. 

 It is doubtful whether such conditions obtain indoors, and the presence 

 of this flea indoors is probably due to introduction by rats which live 

 in the coffee plantations. It may be noted that P. ahalae is absent 

 in houses in districts where there are no coffee plantations or woods. 

 Difiierences of temperature cannot account for this inability of P. 

 ahalae to develop indoors and differences in moisture — due to the great 

 amount of shade in the plantations — may probably be the cause of it. 

 This accords with the statement by Swellengrebel, that the P. ahalae 

 index is much more dependent on the humidity of the atmosphere 

 than the Xenopsylla index and that Pygiopsylla rapidly decreases in 

 numbers after the rainy season. From the above results, the conclusion 

 is arrived at that the species of flea may, to a certain extent, be used as 

 an indicator for the origin of the rats. A high Pygiopsylla index,, 

 when combined with the absence of X. cheopis or with a low X. cheopis 

 index, signifies that the rats come from coffee plantations or woods,, 

 while a high X. cheopis index denotes that the rats have come from 

 the houses. Another conclusion is that a high P. ahalae index of rats- 

 caught indoors, taken in connection with the unfavourable conditions- 

 indoors for the development of P. ahalae, points to a great immigi'ation 

 of wood- and coffee-plantation-rats into the houses. Taking into 

 consideration the great probability of a close intercourse between 



