128 Immunity 



uniform and the method to be employed, provided it is free from 

 error, is that found most convenient to the individual operator. 



The agglutination test now subserves two important functions: 

 I, the diagnosis of any infectious disease, provided the infecting organ- 

 ism he at hand; 2, the recognition of any micro-organism, provided 

 specific serum be at hand. 



Technic of Agglutination Tests 



If possible, a culture of the micro-organism, grown upon agar-agar, is to be 

 selected for the purpose. A good-sized platinum loopful of 'the culture is taken 

 up and distributed as uniformly as possible throughout a few cubic centimeters 

 of distilled water. This is best done by placing the water in a test-tube and then 

 rubbing the culture upon the glass just above the level of the fluid, untU it is 

 thoroughly emulsified, permitting it to enter the water little by little and, finally, 

 washing it all down into the fluid. This gives a distinctly cloudy fluid, too con- 

 centrated to use. Of this one adds enough to each of a series of watch-glasses 

 or test-tubes, each containing an equal voluine of distilled water (say 2 cc), 

 to make the fluid opalescent by reflected light though transparent by trans- 

 mitted light. The same quantity should be added to each, so that they form 

 a uniform series. The patient's blood or serum is next diluted and added so 

 that the watch-glasses or tubes receive' a i : 10, i : 20, i : 30', i : 40, i : 50, 

 I : 60, I : 80, I : 100, i : 150, i : 200, i : 300, etc., respectively, or if an experi- 

 mental laboratory serum of high agglutinative value be used, i : 1000, i : 2000, 

 I : 5000, I : 10,000, I : 50,000, and i : 100,000 respectively. 



If watch-glasses are used, they are stood upon a black surface, covered, and 

 examined in fifteen, thirty, and sixty minutes by simply looking at the dark 

 surface through the fluid. If agglutination occur, the original opalescence gives 

 place to a slightly curdy appearance, as the uniformly suspended bacteria aggre- 

 gate in clumps. 



If test-tubes are employed, they are best observed by tilting them and look- 

 ing through a thin layer of the contained fluid at a dark surface or at the sky. 

 In either case the flocculent collections of agglutinated bacteria' can be seen. 



The test can also be made and observed under the microscope by the hanging- . 

 drop method, but in working with such small quantities much of the accuracy 

 of the technic is apt to be lost. 



Some knowledge is required in order to form correct deductions from the ex- 

 periments. Thus, with typhoid bloods, the agglutination of the typhoid bacillus 

 usually occurs within an hour in dilutions of i : 50, but the agglutinability of 

 the culture employed should be known before the experiment is undertaken. 



Similarly, when the method is employed for the differentiation of bacteria the 

 agglutinative value of the serum should be known to begin with. 



The agglutinins are capable of acting as antigens and when injected into animals 

 effect reactions followed by the formation of antibodies inhibiting their own 

 activity. , 



ANTITOXINS 



Antitoxins are immunity products by which the injurious actions 

 of toxins are annulled. In the synopsis of immunity experiments 

 already given, the history of the discovery and development of the 

 antibodies has been outlined, together with references to the original 

 contributions in which they were made public. 



In the section upon the "Explanation of Immunity" we have 

 seen that the best mode of accounting for the occurrence of antitoxins 

 is afforded by EhrHch in the lateral-chain theory. He regards them 

 as cell haptophiles — receptors — that are formed in excess of the re- 

 quirements, by cells frequently stimulated by the presence of bacte- 

 rial products possessing adapted haptophores. The receptors are 



