20 AIDS TO BACTERIOLOGY 



agglutinins (see Widal Reaction, p. 104, and Saturation 

 Test, p. 152). 



A serum made from one organism may agglutinate 

 bacteria of a closely allied species, but in a less marked 

 manner. 



Precipitins. An antiserum produced by the injection 

 of an animal with a substance containing proteins, if added 

 to a solution of the substance with which the inoculation 

 was performed, causes a cloudiness or precipitate. The 

 test is very delicate, especially when performed as a 

 * ring test ' in tiny tubes. It is used for the detection 

 of horse-flesh in sausages, of castor beans in cattle cake, 

 and for ascertaining the species of animal from which a 

 blood- stain came. The sole drawback to the test is the 

 length of time (up to six weeks) necessary to produce an 

 antiserum. Feeble reactions are also obtained with 

 proteins allied to that used in the production of the anti- 

 serum. 



Antigens. Any substance which, when introduced into 

 the blood, provokes the formation of antibodies for the 

 defence of the organism is called an antigen. Blood- 

 corpuscles, viruses, micro-organisms, etc., are thus all 

 included in the term ' antigen ' without prejudging their 

 nature. The antibody formed through the introduction 

 of an antigen consists of two bodies. One is ' ther- 

 molabile ' (destroyed by a temperature of 55 C.), and is 

 termed an alexin, complement, or addiment. The other 

 body is ' thermostable,' and requires a temperature of 

 75 C. for its destruction. It may be called by various 

 names amboceptor, sensitiser, agglutinin, or precipitin. 

 While the alexin is present in the serum of every animal, 

 whether healthy or diseased, the amboceptor is specific, 

 being peculiar to a particular antigen. 



Haemolysis. If blood-corpuscles be injected into an 

 animal, the blood of the latter acquires hsemolytic proper- 

 ties, and dissolves red corpuscles of the same origin as 

 those which were injected. The solvent agent produced 

 (' hsemolysin ') contains a complement and an amboceptor 

 or immune body. For Haemolysis Test see p. 152. 



Fixation or Absorption of the Complement. Cholera- 

 immune serum, inactivated (i.e., the complement is 

 destroyed) by heating to 56 C. for half an hour, is mixed 

 with the cholera vibrio, when after a time the vibrios are 



