568 Relapsing Fever 



however, against this. It is long, very slender, divides by 

 transverse fission, possesses two terminal flagella, has no 

 undulating membrane, and when most painstakingly stained 

 does not display a major and minor nucleus or centrosome, 

 such as is usually seen in trypanosomes. In favor of the 

 trypanosome theory may be mentioned the occurrence of 

 insects as hosts of the parasites and our inability to grow 

 them upon artificial culture media. 



The organism is undoubtedly the cause of relapsing fever. 

 It can be found in the blood in all cases during the febrile 

 paroxysms and is never found in any other affection. The 

 introduction of it into the blood of monkeys produces re- 

 lapsing fever in these animals, and recently it has been 

 shown by Novy that the organism is usually infectious for 

 white rats. An attack of the disease is followed by immun- 

 ity of long duration, and the serum of rats that have been 

 experimentally infected is protective for other rats. 



