120 
BACTERIOLOGY. 
Luetin 
reaction 
and often lead to the formation of nodules which have 
a tendency to become soft and cheesy. A nodule of 
this sort is called a gumma and is characteristic of the 
tertiary stage of syphilis. The very late manifesta¬ 
tions of syphilis affecting the brain and spinal cord are 
most serious; two of them, general paresis and loco¬ 
motor ataxia are always fatal. 
The presence of syphilis may be detected by ex¬ 
amining the serum from the sores for treponema. 
This may be done by mixing the serum with a drop 
of India ink or, better, by the dark field illumination. 
In either of these methods the treponema appears very 
brilliant in a dark background. This method is par¬ 
ticularly valuable during the first stage while the in¬ 
fection is localized. 
After the infection has been existent for two 
weeks or more the blood serum may be tested by com¬ 
plement fixation or Wassermann test. (See Chapter 
IV, page 42.) 
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, when the complement- 
fixation test is frequently not successful. 
