PROCEEDINGS OF SECTION D. 



519 



livers of these rats, forming extensive, firmish white areas. These ova 

 have a thick double wall with openings at each end, resembling some- 

 what the eggs of Trichocephalus dispar. 



Trypanosoma lewisi. — This Trypanosome is a very common denizen 

 of the blood of Perth rats. It may be found almost as often as searched 

 for. 



Lcucoci/tozoon (probably L. ratti). — This was found once in the 

 mononuclear leucocytes of a rat, strangely enough within a day of 

 reading an account of the discovery of apparently the same species in 

 a rat in Khartoum by Dr. Balfour. Its occurrence here has been 

 recorded in the Journal of Tropical Medicine. Since then another 

 observer has recorded finding apparently this same parasite in Mus 

 rattus in India. 



PREGNANCY IN RATS. 



The usual recurrence of plague in Australia during the first six 

 months of the year, and its comparative disappearance later on, have 

 given rise to much speculation. Extending as it does from hot into 

 cold weather in temperate parts would seem to exclude climatic con- 

 ditions to some extent. Is there any inherent quality in the rats 

 themselves which would tend to cause the epizootic to die out amongst 

 them in the infected area ? Undoubtedly all rats affected with plague 

 do not die. Those that recover would be immune to a greater or less 

 extent, and of the others some might be naturally very resistant to the 

 disease. If this is the case, then plague might be expected to recur 

 when young non-immune rats had to some extent replaced the loss 

 caused by the epizootic, provided a few of the previous generation were 

 able to hand on the disease to them. It has, therefore, seemed to me 

 to be important to ascertain if possible whether any particular month 

 of the year is especially a breeding time for rats. I give the proportion, 

 for eight months, of pregnant females to adult non-pregnant females, 

 though fullv recognising that the figures are far too small to be trust- 

 worthy. Their presentation may, however, stimulate others to go 

 more fully into the matter, with perhaps interesting results. 



