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On Rickettsia 
(3) Observations on other Species of Rickettsia. 
Being unable to obtain additional cases of trench fever owing to its 
gradual disappearance after the war, a number of insects from various sources 
were examined in order to see whether other species of Rickettsia could be 
found. 
Rickettsia melophagi. 
Through the kindness of Messrs Cooper, Sons and Nephew, Watford, large 
numbers of Melophagus ovinus were obtained from sheep in various parts of 
the British Isles. The examination of these sheep-keds revealed the presence 
of Rickettsia in the alimentary canal of a large proportion of these insects. It 
seems to be fairly widespread for in addition to Germany, where it was noticed 
by Noller (1917) and Sikora (1918), I have found it in Melophagus from 
various parts of England, Scotland and Ireland. 
R. melojphagi closely resembles R. quintana, both in its morphology and 
method of multiplication. The organisms are especially abundant in the middle 
and hinder region of the stomach, where they often form a layer on the surface 
of the epithelium. It is difficult to be certain that they do not penetrate into 
the cells themselves, but the appearance of sections suggests that they only 
occur on the surface in the same way as R. quintana. The organisms pass to 
the outside together with the faeces and presumably the infection is thus 
transmitted from one Melophagus to another. 
According to Sikora (1918) Rickettsia melojphagi is transmitted hereditarily 
to the offspring of infected Melophagus, in which case it is evident that the 
organisms must have the power of passing through the tissues and invading 
the ovaries or testes. The examination of sections of the developing ova 
resulted in finding a few bodies that might have been Rickettsia, but when 
present in small numbers it is difficult to distinguish them with any certainty 
from artefacts and therefore the results were inconclusive. However, the 
presence of Rickettsia in the young offspring of infected Melophagus, renders 
it probable that this infection is hereditary. 
The Rickettsia were frequently associated with Crithidia melophagi and 
occasionally a parasitic nematode was also found in the alimentary canal of 
the Melophagus. 
Rickettsia trichodectae n. sp. 
The examination of Mallophaga from the horse resulted in the discovery 
of Rickettsia in 7 to 8 per cent, of the lice examined. The species of Mallophaga 
was Trichodectes pilosus and the presence of a Rickettsia in these insects is 
especially interesting as they do not feed on blood, and therefore cannot 
acquire the infection by the ingestion of infected blood. 
The parasites occur in the alimentary canal of the Trichodectes and closely 
resemble Rickettsia melophagi in their morphology. Their dimensions are about 
Oo-O-5/x in diameter by about 0-5 to 0-9fi in length and occasionally longer 
