ANIMAL MICRO-PARASITES. 599 



H^MATOZOA OF RATS. 



In describing these organisms, Lewis remarked that it wa& 

 strange that they had not occupied attention before, and suggested 

 as an explanation that possibly European rats did not harbour these 

 parasites. The author examined a few white rats, but without 

 success, and then proceeded to examine the blood of common brown 

 rats, trapped from the London sewers, and discovered 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 filaments 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 granu- 

 larity, and they were more un- 

 dulatory in movement than FlG . 23 9.._p ARASITE8 IN THK BLOOD 

 spirilla. A corpuscle might be OP RATS (Lewis), 



observed to quiver, and this 



could be distinctly traced to be due to the existence of a flagellum, 

 apparently a posterior flagellum, as the organisms seemed generally 

 to move with the thicker end forward; no flagellum could be 

 detected at the opposite end. The greater number of the figures- 

 in the woodcut (Fig. 239) are described as representing these 

 organisms a few hours after the blood had been obtained, when 

 their movements are not so rapid, and the flagellum becomes more 

 easily recognisable. 



This observation led Kent, who named the organism Herpetomonas 

 Lewisi, to remark that if, as Lewis is inclined to maintain, that 

 organ " propels instead of draws the animalcule through the in- 

 habited serum, we have presented a structural and functional feature 

 without parallel among the other representatives of these Protozoa 

 flagellata, the recognition of which would demand the creation of a 



