684 INFECTION AND IMMUNITY, 



this way is very temporary and is to be referred 

 to a reaction caused in the body rather than to a 

 direct effect on the parasites. The latter are not 

 killed by the dye in test-tube experiments. "One 

 may conceive of the action of a trypanroth in this 

 way, that as a result of a fresh injection of the 

 dye a reaction takes place in the animal's body, 

 which leads to the death of the trypanosomes ; the 

 reaction products possess only a temporary char- 

 acter and cease to be formed as soon as the dye 

 is disposed of." 



Laveran reports a favorable influence on try- 

 panosomiasis in mice and rats by a combined treat- 

 ment with sodium arsenite and "trypanroth." 



When a dose of trypanroth which is insufficient 

 to cause complete disappearance of trypanosomes 

 is given, the remaining organisms become immune 

 to the further action of the drug. It is of impor- 

 tance, therefore, to give the largest dose which is 

 non-toxic for the patient. At present, two new 

 preparations of Ehrlich, trypanosan and agridi- 

 num, which are highly trypanocidal, are being 

 tried in combination with arsenophenylglycin. 



III. TEXAS FEVER. 



Texas fever of cattle may be considered briefly as a 

 well-established example of piroplasmosis. 

 The Th. Smith and Kilbourne (1893) discovered a pear- 

 Parasite, shaped protozoon (Pyroplasma bovis) , which occurs in 

 pairs in the erythrocytes of infected cattle. The para- 

 site measures from 2 to 4 microns long by 1.5 to 2 

 microns broad, the smaller ends of the pairs lying in 

 apposition. The organisms have a rapid but rather coarse 

 ameboid movement. About 1 per cent of the corpuscles 

 are invaded ordinarily, but in fatal cases the proportion 

 may rise from 5 to 10 per cent. The method of prolifera- 

 tion of the parasite has not been followed out definitely. 



