116 J. B. CLELAND. 
selective in their behaviour, no longer being merely faculta- 
tive parasites of the two types of hosts, but obligatory para- 
sites of both, with perhaps complicated life-histories in 
each. 
I have mentioned Sp. ratt1 as a probable saprophyte of 
the intestinal canal of rats. The spirochetes (Sp. actero- 
hemorrhagica Inada and Ino) of a form of infective jaun- 
dice (Weil’s Disease) in man and those (Sp. morsus-muris 
Futaki, Takaki, Taniguchi et Osumi) found in rat-bite 
fever in man and other animals, appear to be normally para- 
sites of rats, occasionally conveyed to man with severe, 
even fatal, results. These diseases are dealt with else- 
where. 
The Helminth Parasites of Rats and Mice. 
NEMATODES.—Hall' gives the recorded numbers of species 
of nematodes in Hpimys norvegicus as 11, in EH. rattus (if 
E. alexandrinus is included) as 12, and in Mus musculus as 
12. Of the species found in HZ. norvegicus and E. rattus, five 
are common to both. M. musculus shares three species with 
E. norvegicus and four with EF. rattus, whilst two species 
are common to all three rodents. 
Harvey Johnston? records the various species of hel- 
minths found in rats and mice in Australia. Six nematode 
species have been found in H. norvegicus, 5 in EL, rattus, 
and 5 in M. musculus. Consideration of this paper requires 
the addition to Hall’s list, to make it complete, of Hepatt- 
cola hepatica and Heterakis spumosa for Mus musculus, and 
of Oxyuris obvelata for Epimys norvegicus. Johnston also 
records Cisophagostomum sp.° for EH. norvegicus, whilst in 
2 Maurice Hall, Nematode Parasites of Mammals of the Orders 
Rodentia, Lagomorpha and Hyracoidea, Proc. U.S. Nat. Mus., 1916, 
p. 227. 
2 Johnston, Rep. Bur. Microbiol., Syd., 1909 (1910), and Proc. Roy. 
Soc., @,, 1912,;.p, 107, and 1918, p.-53, in the press: 
3 Since identified by Johnston as Heligmosomum braziliense ‘Trav. Proc. 
Roy. Soc., Q., xxx, in the press. 
