266 IMMUNOLOGY 



Summary. — A few of the important points brought out in this 

 chapter as well as some additional information may be sum- 

 marized as follows: 



1. Diphtheria is essentially a toxemic disease. To produce it 

 the organism, C. diphtherioe, must be able to establish itself and 

 create favorable conditions for the production and absorption of 

 toxin. While all strains produce qualitatively the same toxin, they 

 differ iti the amount they can produce, in their invasive power, 

 and perhaps in their oxygen requirements. 



2. Man seems to be the one naturally susceptible host, although 

 the disease can be produced experimentally in guinea pigs, dogs, 

 and many other animals. Mice and rats are refractory to experi- 

 mental intoxication with diphtheria toxin. Their resistance seems 

 to depend upon tissue insusceptibility rather than antitoxin. Im- 

 munity in man is due largely to antitoxin although tissue resis- 

 tance to invasion and adsorption of toxin may play some part in 

 natural immunity. 



3. The units of measurement of toxin are the minimal lethal 

 dose (M.L.D.), minimal reacting dose (M.R.D.), limit of reaction 

 dose (Lr), limes nul or threshold dose (Lo), limes Tod or death 

 dose (LJ, flocculating dose (Lf) and the Schick skin test dose 

 (1/50 M.L.D.). These are defined and discussed. Ehrlich intro- 

 duced the units that involve death or protection against death 

 as end points while Eomer introduced a method of measuring 

 toxin in terms of the amount necessary to produce a skin reaction. 

 Modifications of his technic have formed the bases of the skin 

 test units such as the M.R.D., Lr and Schick test dose of toxin. 

 The technique of the Ramon flocculation test and method of dc- 

 tennining the Lf dose of toxin and the mechanism of the reaction 

 are also discussed. 



4. Diphtheria toxin like all true toxins is an antigenic poison. 

 It is probably secreted by C. diphtherme. According to Eaton it 

 does not appear to be either a cleavage product from the media nor 

 a toxic radical attached to a protein. 



When in solution it is relatively thermolabile, being destroyed 

 when heated to 60° C. for thirty minutes. Dried toxin with- 

 stands 100° C. but is destroyed at 150° C. 



