420 THE AGGLUTINATION TEST. 



where agglutinin production is very marked. The amount of 

 agghitinin present in an animal's serum is no index of the degree 

 of imnumity possessed by the animal, and it may be immune 

 to a disease after it has lost the power of agglutinating the 

 organism which caused the disease — in fact, agglutinin pro- 

 duction only continues as long as the organism is in the body. 



Agglutinins are thermo-stable antibodies, which means that 

 thev will resist heating to 56° C. for half an hour without losing 

 their properties. At a temperature of between 62° C. and 70° C. 

 they become what is called agglutinoid, which means that they 

 combine with the bacteria without causing them to clump at all. 

 Curioush- enough, it has been noticed by Dreyer that agglutinoid 

 when boiled for an hour or longer will regain the power of 

 causing agglutination of bacteria. The fact that agglutinoid 

 combines with the bacteria is easily proved by adding a serum 

 Avhich has been heated to 70° C. for half an hour to an emulsion 

 of bacteria. The mixture is centrifugalised, and the sedimented 

 bacteria are taken away and added to a fresh serum which is 

 known to agglutinate the species of bacterium which is being 

 used "^n the experiment. No agglutination will now take place. 

 l)roving that the bacteria have combined with the agglutinoid. 

 and cannot, therefore, take up agglutinin. 



Agglutinins are relatively highly resistant bodies. They 

 will stand drying for months even when fully exposed to the 

 air. Light has little effect on them, and putrefaction even in 

 a marked degree causes very little loss of agglutinating power. 

 This resistance is in very marked contrast to that possessed by 

 most of the other antibodies [produced as a result of bacterial 

 invasion or existing naturally in the serum of an animal. Normal 

 sera often possess agglutinins, which in these cases would be 

 natural. The horse's serum is very rich in them, and will 

 often clump the bacillus of glanders when diluted 300 times, so 

 that when the agglutination test is applied for the diagnosis of 

 this disease this natural antibody is allowed for, and only a horse 

 whose serum. >vhen diluted 500 to 1,000 times, will still agglu- 

 tinate the glanders bacillus can be considered to be suft"ering 

 from the disease. Very feeble agglutinating powers have been 

 observed in the serum of young animals, and even fcetal blood 

 has been shown to possess them in some slight degree. Natural 

 agglutinins are probably produced as a result of sub-infection 

 from the intestines, or bv mild attacks of disease which pass 

 unnoticed. A fairly strong agglutinating serum has been 

 observed in a three-weeks old calf which was born to a cow 

 which had become infected with the contagious al)ortion organ- 

 ism, and whose serum would agglutinate it in a dilution of 

 I :i,ooo, though the cow did not actually abort. The serum 

 of the calf agglutinated in a dilution of i :200, the limit of normal 

 agglutination in this disease being put at i :50. By inoculating 

 an animal with an organism a tremendously powerful agglu- 

 tinating serum can be produced. Such a serum is ]-)roduced by 



