PART III.] Two Species of Rats in which the Organisms are Found. 607 



ammonia did not aflfect them for some time, but a stronger solution of potash affected 

 such of them as it came into contact with at once : others in the middle of the field 

 continued to exhibit movements for several hours ; probably they had not been touched 

 by the potash. A weak solution of bichloride of mercury in acetate of potash and 

 camphor water (as used for preserving preparations) did not seem to affect them ma- 

 terially, seeing that they maintained their activity in such a solution for eight hours. 

 They retain their vitality longer in a weak salt-solution than in pure distilled water. 

 A cover-glass with an aqueous solution containing them was inverted over a bottle of 

 chloroform for several minutes, but the movements of the organisms were unaffected ; 

 if, however, a drop of blood containing them be similarly placed over chloroform they 

 disappear, probably owing to the action of the chloroform-vapour on the blood itself. 



A drop of the blood was placed on a slide arranged for the application of elec- 

 tricity to microscopic preparations, and it was found that an interrupted current of 

 such a strength as could not be comfortably borne by an individual was tolerated by 

 these beings for several consecutive hours. The only difference appreciable between a 

 preparation thus dealt with and one not so treated was, that the movements ceased 

 a few hours sooner in the former than in the latter, possibly owing to the chemical 

 change induced in the blood itself by the current, 



I have examined the blood of a great number of rats for the purpose of ascer- 

 taining what proportion of them contains these organisms in their blood, and find 

 that of those specially examined for this purpose their existence was demonstrated in 

 29 per cent. Sometimes, however, the numbers detected were very few, not more 

 than one or two in a slide, but in the greater number of cases they were very 

 numerous, every slide containing several hundreds. 



Being anxious to ascertain precisely the species of rats in which these organisms 

 were found, I consulted an accomplished naturalist. Dr. John Anderson, Superintendent 

 of the Indian Museum, and he was so good as to identify the specimens for me from 

 time to time. The result has been that it has been definitely ascertained that these 

 organisms may be found in two species, viz.^ Mus decumanus and Mus rufescens. 



It would appear that they are not found in mice. I have examined the blood of 

 a large number, but never detected any organisms of the kind ; nor have I seen them 

 in any animals other than rats. 



It is possible that these minute organisms ought to have been described in the 

 part of this paper devoted to the description of microphytes, as they present many 

 features in common with motile organisms undoubtedly of vegetable origin; on the 

 other hand, taken as a whole they appear to approach more closely to the forms of 

 life usually classified as protozoa; such, for example, as several of the species of 

 Dujardin's genus Cercomonas. It should, however, be noted that many believe that 

 these organisms are zoospores and not animalcules. 



The nearest approach to a description of these haematozoa which I can find is in 



