596 A MANUAL OF BACTERIOLOGY 



is conveyed by direct contact, and is mainly confined to the 

 lesions, being scanty in the blood. It is pathogenic to the 

 ordinary laboratory animals. 



In rats a non-pathogenic trypanosome was found by Lewis 

 (Tr. Lewisi). It is especially met with in sewer-rats, but also 

 occurs in field-rats (Crookshank). It is somewhat shorter and 

 thinner than the Tr. Brucei, and there are other small differences 

 between the two forms. With the exception of rats and mice, 

 and to a less extent guinea-pigs, other animals cannot be infected 

 with the Tr. Lewisi. It may be kept alive for long periods in the 

 blood placed in a refrigerator, whereas the Tr. Brucei soon dies 

 under the same conditions. The two forms do not protect 

 against each other. The Tr. Lewisi is readily cultivated on 

 rabbit-blood agar and is transmitted by the rat-flea, in which it 

 seems to penetrate into the epithelial cells of the gut and there 

 undergoes a process of multiplication. 1 It is passed in the faeces 

 of the flea, and a rat ingesting the infected faeces becomes infected. 



A number of other trypanosomes have been found in the lower 

 animals, birds, fish, reptiles, and amphibians. A large and 

 characteristic one is generally present in the blood of the eel. 



The trypanosomes are usually agglutinated when mixed with 

 the serum from an infected animal. 



Hewlett was unable to obtain any toxic or immunising sub- 

 stance from ground-up trypanosomes (Tr. Brucei}: 1 



Levaditi and Twort 3 found that the filtrate of broth 

 cultures of B. subtilis is markedly trypanocidal in vitro but not 



Examination of Flagellates and Ciliates 



(1) Trypanosomes, if numerous, are readily observed in the 

 fresh blood. A very shallow cell may be formed on a slide by 

 ringing with melted paraffin. For stained preparations the 

 Leishman stain (see "Malaria") or the Heidenhain method 

 (p. 587) may be employed. 



(2) Other Flagellates and Ciliates may be examined fresh in 

 the fluid in which they are present, by mounting on a slide, and 



1 Minchin and Thompson, Brit. Med. Journ., 1911, vol. ii, p. 361. 



2 Proc. Roy. Soc. Lond., B, vol. Ixxxiv, 1911, p. 56. 



3 Comp. Rend. *S T oc. BioL, vols. Ixx and Ixxi, 1911. 



