GROUP AGGLUTINATION. IOI 



by vaseline, and examined microscopically. A control with normal serum 

 and also one with culture alone should be made. 



For the identification of bacteria only highly agglutinating 

 Production of animal sera can be employed. Rabbits, goats and horses, 

 Agglutinating are most suitable for such experiments. The best results 

 Sera. are obtained when the animals are immunized intravenously 

 by repeated injections with gradually increasing doses of dead 

 bacteria (killed at 60 C.). Usually two to three injections of 1/4 to i agar 

 culture suffice to give an agglutinating titer of i to 5000. The serum 

 should be withdrawn eight to ten days after the last injection. As a matter 

 of course the titer of the serum should be tested from time to time, because 

 the height of the titer curve can only reach a certain point. When a suffi- 

 cient strength is obtained the animal is bled. It is not possible to produce 

 equally strong agglutinating sera for all bacteria. 



The agglutinins belong to the class of the more resistant serum sub- 

 stances. With slight addition of carbolic acid they can be preserved on ice 

 for a long time. Heating, variously affects the different bacterial agglu- 

 tinins. The agglutinins for pest and tubercle bacilli are destroyed at 56 C. 

 while other bacteria are not influenced by even higher temperatures. The 

 animal from which the agglutinating serum has been obtained also influences 

 to a great degree, the resistance towards heat. Thus the typhoid agglu- 

 tinating serum derived from the horse is much more resistant than that 

 obtained from the rabbit. 



The Microscopic (Orientation) Agglutination Test. 



This method is especially of use, when only small amounts of culture 

 or serum are obtainable. Also, if agglutination is employed for the quick 

 recognition of bacteria, as for example, when it is desirable to know whether 

 a blue colony on a Conradi-Drigalski-agar plate is typhoid or not. 



In such a case a drop of the immune serum in the dilution of 1 150 or i :ioo 

 is placed upon a cover-glass held with a Cornet's forceps, and a small part of 

 the bacterial colony for identification carefully mixed with this serum. As 

 controls, a mixture is made with salt solution and with normal serum. If 

 agglutination occurs, small granules or clumps can readily be seen with the 

 naked eye by holding up the cover-glass against the light. The control 

 glasses on the other hand should show only a homogeneous turbidity. 

 These changes are still more evident if the mixture is examined micro- 

 scopically in the form of a hanging drop. (Described, p. 100.) 



Group Agglutination. 



On testing the titer of a strongly agglutinating typhoid serum, and a 

 strongly agglutinating cholera serum, against typhoid, paratyphoid, colon and 

 cholera bacteria, the results will appear to be the following: 



