8 SCIENCE PROGRESS. 



question that presents itself here is this : is this production 

 of immunity clue solely to the formation of antitoxin, due to 

 stimulation by the toxins elaborated by the microbes in the 

 body, or is it also due to the presence of substances derived 

 from the microbes themselves ? As the disease passes orf 

 the microbes themselves degenerate and disappear as such, 

 and subsequent infection of the body with the microbes 

 does not succeed at all, as in complete acquired immunity, 

 or succeeds only partially and after large doses, as in 

 moderate degrees of acquired resistance. It stands to 

 reason that the substance of the degenerating bacterial 

 bodies contributes something towards the acquired re- 

 fractory state of the blood and tissues, and as a matter of 

 fact it has been shown (Klein, Sobernheim) that the 

 substances of bacteria (intracellular substances) possess in 

 sufficient doses an inhibitory action, inasmuch as they are 

 capable of furnishing the tissues with a refractory power 

 against the subsequent growth and multiplication of the 

 microbes. The assumption, therefore, that the presence of 

 bacterial intracellular substances in the blood and tissues of 

 an animal, after the disease has passed and after the bacteria 

 that caused the disease had degenerated, plays some part in 

 the condition of resistance against a subsequent invasion 

 and multiplication of the specific bacteria, is at least a 

 justified one. Fraenkel showed that in cultures of diphtheria 

 bacilli there are two substances present : one the toxin 

 destroyed by heating to 60-70° C, and another the 

 immunising substance not destroyed at 60-70 C. ; it is quite 

 feasible to assume that this latter owes its origin to and is 

 identical with the bacterial substances themselves ; moreover 

 he showed that if a culture be heated to 6o°-7o C. (whereby 

 the toxin is destroyed), and then injected in sufficient quan- 

 tities subcutaneously into the guinea-pigs, these latter, after 

 the lapse of at least fourteen days, are protected against a 

 second injection with a fatal dose of living bacilli. The lapse 

 of at least fourteen days is very suggestive for the above-ex- 

 pressed view, that the bacteria eventually yield substances 

 which form one of the elements of the immunising action. 



When an animal acquires resistance by repeated injec- 

 tions with gradually increasing doses of diphtheria toxin, 



