38 IMMUNE SERA 



of it as the "Gruber-Widal reaction," whereas in 

 the beginning only the term " Widal reaction " 

 was used. 



The manner in which the reaction proceeds in 

 microscopical preparations as well as when mac- 

 roscopically observed has been described above 

 (page 32). Nowadays the microscopic method is 

 given the preference x because in many cases it is 

 distinct when the macroscopic reaction fails; and 

 further because the former yields distinct results 

 within an hour at the most, whereas in many cases 

 twenty-four hours are required for the macroscopic 

 test. 



Pfaundler's Reaction (Thread Reaction). It 

 may be well at this point to call attention to a 

 peculiar reaction described by Pfaundler 2 in 1896. 

 This author showed that certain bacteria, though 

 they might not be agglutinated by a given serum, 

 would often, when they were grown therein, develop 

 in the form of long threads more or less interlaced. 

 This occurred only in the specific serum and wa 

 absent in the normal serum. Most authorities 

 regard the thread reaction as a manifestation of 

 agglutinins. According to Metchnikoff this reaction 

 sometimes gives more information concerning a 

 serum than does the ordinary agglutination test. 



1 This applies to typhoid ; in other diseases the macroscopic 

 method is sometimes preferable, 



'* Pfaundler, Centralblatt Bacteriologie, Vol. xix, 1896. 



