IMMUNITY AND IMMUNIZING AGENTS. 



119 



opsonogens) which in some instances have given excellent results. It has 

 also been found that substances other than opsonins may increase phagocy- 

 tosis, as for example, nucleinic acid and coUargol. 



From the foregoing it becomes evident that immunity from disease 

 depends upon the presence in the body of antitoxins, bacterolysins, and the 



YiG, 53. Opsonic Incubator. The determination of the Opsonic Index has become 



so important that these incubators have been made to meet the demands for an 

 apparatus in which twenty pipettes can be incubated at one time, and so that any tube may 

 be examined during the progress of the experiment without changing the temperature of 

 the others. There are twenty tubes for opsonic pipettes and an extra tube. The tubes 

 may be easily removed when desired by means of a key which accompanies the incubator. 

 On top there are eight tubes, 22 mm. in diameter, for test-tubes. Each is provided with a 

 nickel-plated cap. The incubator is supplied with thermometer, thermo-regulator, and 

 a two-flame burner, with wire guard. 



opsonins vi^hich induce phagocytosis. It is furthermore possible to increase 

 the activity of these agents artificially. All three agents are specific in 

 nature as already stated. Ehrlich has attempted to explain the phenomena 

 of immunity according to his receptor or side chain theory (Seitenketten- 

 theorie). This theory, w^hich is rather complex and highly technical, was 

 first used to explain cell metabolism. Hinman's version of the side chain 

 theory is very simple and we give it as follows: As applied to immunity 

 the basis of the theory is the conception of the duplex nature of antigens. 



