igog.] R- B. Lloyd : The Races of' Indian Rats. 83 



Rangoon bandicoot is much smaller than the Madras one, the grey 

 rat can exist though it does not flourish as in Bombay and Calcutta. 



In the last report of the Plague Commission it was shown that 

 Mus decumanus was the species which in Bombay had a preponderat- 

 ing influence in plague dissemination. Certain conclusions may 

 be quoted from the report {Journal of Hygiene, vol. vii, No. 6). 



'' With regard to the epizootic amongst the rats, the following 

 conclusions may be formiilated : — 



(i) Mus decumanus and Mus rattus are equally susceptible to 

 plague. 



(2) The incidence of plague is twice as great on the decu^ 



manus population as on the rattus population, 



(3) Mus decumanus is the species which is chiefly respon- 



sible for the diffusion of plague amongst the rats 

 throughout Bomba)'" city. 



(4) The decumanus epizootic precedes the rattus epizootic 



by a mean interval of about ten da3^s. 



(5) The rattus epizootic is directh^ attributable to the de- 



cumayius epizootic. 



(6) Plague persists in the rats in Bombay' city during the 



off season. This persistence is due chiefly to Mus 

 decumanus.^' 



The conflicting natures of the first and second statements are 

 reconciled and explained b}' the fact that Mus decumanus, on an 

 average, harbours twice as man}'' fleas as Mus rattus. 



It seems, therefore, that Mus decumanus is an important 

 factor in the sanitation of a port. After reading the conclusions 

 quoted above, anyone must be struck with the coincidence that 

 ^ladras, the one port which does not harbour Mus decumanus, is 

 the one port which has never been seriously infected with plague. 

 That ^Madras is not wholly protected by its climate is shown by the 

 fact that there has been at least one outbreak of plague, temporary 

 but severe, on the outskirts of the city.^ On the other hand, it 

 must be remembered that plague persists to a grievous extent 

 among certain provinces of India into which Mus decumanus seldom 

 or never penetrates. 



The insanitary effect of decumanus as a port rat can be seen 

 from another point of view. In a port where this rat is firmly 

 established, there must be much more interchange between ship 

 and shore rats than in a port like Madras, where the large bandicoot 

 alone is the common outdoor rat, for the bandicoots probably never 

 enter ships, whereas Mus decumanus is perhaps the commonest 

 of all sea-going rats. It has not 3^et been thoroughly ascertained 

 to what extent the different species of rats infest ships plying in 

 tropical seas. Judging from very scant}' observations and inquiries 

 it appears that any one ship harbours only one species at a time 

 — sometimes Mus raUus, sometimes decumanus. A thorough in- 

 vestigation of this subject would be interesting and important. 



1 If, as appears, the bandicoots themselves are particularly susceptible to 

 plague, the absence of Mus decumanus from Madras is of no significance. 



