IQ2 MANUAL OF BACTERIOLOGY. 



with other bacteria than the bacilli of typhoid fever. The 

 nature of this agglutinating substance, as it is called, is not 

 known nor is its significance understood. It has been 

 applied to the diagnosis of typhoid fever, where it is called 

 the " serum-reaction," and will be discussed in connection 

 with the bacilli of typhoid fever. Similar agglutinating 

 bodies form in many other infections. Bacteria that are not 

 motile may nevertheless be agglutinated. Among the in- 

 fections where such a reaction occurs, the following are 

 noteworthy with the cholera spirillum, bacillus pyocya- 

 neus, bacillus proteus, bacillus coli communis, micrococcus 

 melitensis, bacillus of glanders, bacillus tuberculosis, diplo- 

 coccus of pneumonia, bacillus of bubonic plague, and the 

 bacillus of dysentery (Shiga). The protozoon, Try- 

 panosoma (see appendix), is said to become agglutinated 

 in the blood of infected rats. Not all of these have been 

 studied sufficiently to be available for diagnostic purposes. 

 It has not yet been shown that agglutinins are concerned in 

 producing immunity or recovery from infectious diseases. 

 These substances are relatively resistant to heat, not being 

 destroyed by temperatures below 70 C. 



Under conditions similar to those under which agglutina- 

 tion occurs, bacteria have been observed to form in long 

 filaments. This is the so-called " thread-reaction." Its sig- 

 nificance is uncertain. 



Precipitins. After repeated injections of albumins for- 

 eign to it, an animal's fluids undergo still another form of 

 adaptation. Substances are now developed in the blood- 

 serum, which cause precipitates to form where it is mixed 

 with the foreign albumin. 1 Thus a rabbit may be immu- 



1 These reactions have been most fully studied in connection with the 

 precipitation of blood-serum of a particular animal by the serum of 

 another species which has been immunized to the serum of the first 

 animal. The principle is of some importance in medico-legal work 

 for the identification of human blood, as in stains on clothing. See 

 Nuttall, Journal of Hygiene, Vol. I., 1901. 



