484 A MANUAL OF BACTERIOLOGY 



small amoebae is formed. Instead of encystment, as in 

 the E. coli, resistant spores are formed. The nucleus gives 

 off chromidia, some of which, together with portions of the 

 ectoplasm, are extruded and become spores surrounded 

 by tough capsules. Infection of a fresh host apparently 

 occurs only with material containing these spores. 



The presence of the amoeba in the pus, and especially 

 in the walls, of tropical abscesses is of considerable diag- 

 nostic significance, and the parasite is considered to be 

 the etiological agent in amoebic or tropical dysentery 

 (see " Dysentery "). The amoebae are not usually observed 

 in the abscess pus at the time of operation, but make 

 their appearance in the discharge about the third day, 

 i.e. when the wall of the abscess- cavity is contracting. 

 In the true tropical abscess the ordinary pyogenic organ- 

 isms are absent, unless a secondary infection has occurred, 

 which is the exception. The abscess is usually single, and 

 Rogers suggests that the amoebae reach the liver through 

 adhesions between it and the bowel. The amoebae may 

 be cultivated on ordinary or on water agar provided some 

 bacterium is present at the same time, e.g. B. coli, cholera 

 vibrio, etc. Material rich in amoebae may be smeared 

 over agar plates, which are grown at 25-30 C. for twenty- 

 four to forty- eight hours, and are then examined with a 

 low power. At any spot where isolated amoebae are 

 observed, with a little dexterity the organism may be 

 lifted up with a fine needle and transferred to a fresh 

 plate, and by a repetition of the process pure cultures 

 may be obtained. The cultivated amoebae are pathogenic 

 for monkeys, and induce abscess on inoculation into the 

 liver. Musgrave and Clegg (loc. cit.) are of opinion that 

 all amoebae are, or may become, pathogenic. 



