116 BACTERIOLOGY. 



which have a tendency to become soft and cheesy. A 

 nodule of this sort is called a gumma and is character- 

 istic of the tertiary stage of syphilis. 



Diagnosis The presence of syphilis may be detected by 



examining the serum from' the sores for spirochetes. 

 This is done by mixing the serum with a drop of india- 

 ink, which makes the colorless spirochetes easier to 

 see. A better method, and one now in general use, 

 is the Wassermann reaction, which aims to detect the 

 presence of the immune substances that develop in the 

 blood soon after infection has taken place. The 

 technique of the reaction is complicated and will not 

 be taken up here; suffice it to say that it is successful 

 in from 90 to 95 per cent, of the cases. 



Killed cultures of the spirochetes may also be 



utilized in diagnosis by injecting a very small amount 

 of the culture into the superficial layers of the skin. 

 This is called the luetin test, and was devised by Dr. 

 Noguchi. A successful or positive test is shown by 

 the development of a hard, inflamed nodule at the 

 point of injection, and is due to the hypersensitiveness 

 of the skin to the syphilitic poison. The test is of value 

 only in the later stages of the disease. 



THE SPIROCHETE OF RELAPSING FEVER. 



The cause of relapsing fever is a group of spiro- 

 chetes, the individual members of which differ in 

 minor details in the various countries where the dis- 

 ease prevails. The spirochetes are long, delicate 



