922 Transactions of the Society. 



changes form by sending out processes laterally, and contains two 

 to four refractive spherules. Blood of mud-fish. 



Htematomonas carassii. — Long bodies, with narrow membrane 

 attached along the whole length; less actively motile. Several 

 forms also observed strikingly smaller than the above ; many disc- 

 shaped. Often seen attached to a red corpuscle, setting them in 

 motion by their movements. Blood of carp. 



From my observations of the Surra parasite (especially the dis- 

 covery of the undulating longitudinal membrane) I recognized a 

 very close resemblance to Mitrophauow's descriptions, and concluded 

 that if we followed the classification adopted by Mitrophanow his 

 genus of HcTtnatomonas must not be restricted to organisms in fish- 

 blood. It must be expanded to include this parasite of mammalian 

 blood, which should in that case be named Ilxmatomonas Evansi 

 rather than Spirochzeta Evansi as proposed by Steel. 



I now revert again to the flagellated organisms observed by 

 Lewis. The different impression conveyed to me by his photo- 

 graphs on the one hand and his woodcuts on the other, led me to 

 desire to investigate this organism for myself; and moreover it 

 promised to afford me a new object for work I had recently brought 

 before the Society, namely, the photography of flagella. In speak- 

 ing of these organisms, Lewis remarked that it was strange 

 that they had not occupied attention before, and suggested as an 

 explanation that possibly European rats did not harbour these 

 parasites. My first thought was to obtain some rats from India, 

 but it occurred to me it would be interesting to make sure that 

 these parasites were not found in Europe. I therefore examined a 

 few white rats without success and then proceeded to examine the 

 blood of common brown rats, and in some, to my astonish- 

 ment, I found that it teemed with exceedingly active organisms. I 

 immediately obtained a large number of brown rats trapped from 

 the London sewers, and 1 have ascertained that these organisms 

 are to be found in no less than 25 per cent, of apparently healthy 

 animals. The first question which naturally arose was whether 

 these organisms in European rats were identical with those 

 described by Lewis in Indian rats. 



If we refer to the description given by Lewis, we find that 

 he states that when he first noticed them he thought they 

 were vibrios or spirilla. The drop of blood under examination 

 appeared to quiver with life, and on diluting the blood, motile fila- 

 ments could be seen rushing through the serum and tossing the 

 blood-corpuscles about in all directions. 



The filaments were pale and translucent, without any trace of 

 visible structure or granularity, and they were more undulatory in 

 movement than spirilla. A corpuscle might be observed to quiver, 



