THE BACILLUS AND THE BACTERIOLOGY OF DIPHTHERIA 215 



culture is usually removed a toxin which usually grades Ehrlich's 

 antitoxin within 5 per cent, of the strength given by him. 



We believe that by using such a bacillus we can, after gaining a fuller 

 knowledge of its characteristics, obtain a toxin of a known and suitable 

 neutralizing value, and thus always correctly standardize an antitoxic 

 serum in case the present stations ceased to supply a testing serum. 

 This is certainly true for the bacillus which we have used for the 

 past ten years. A preparation of a carefully tested antitoxin is of 

 immense value in ensuring a uniform standard among the different 

 testing stations and in allowing of comparison between them. 



The old definition of Behring and Ehrlich, that an antitoxin unit 

 contains the amount of antitoxin which will protect the life of a guinea- 

 pig from one hundred fatal doses of toxin, must be modified so as to 

 be defined as that amount of antitoxin which will neutralize one hun- 

 dred fatal doses of a toxin similar to that adopted as the standard 

 namely, one having approximately the characteristics of toxins in cul- 

 tures at the height of their toxicity. 



The actual test of an antitoxin serum is, therefore, carried out as 

 follows: Six guinea-pigs are injected with mixtures of toxin and anti- 

 toxin. In each of the mixtures there is 100 times the amount of a toxin 

 such as just described, which will kill 250 grm. of guinea-pig on an 

 average in ninety-six hours. In each of the mixtures the amount of 

 antitoxin varies; for instance, No. 1 would contain 0.002 c.c. serum; 

 No. 2, 0.003 c.c.; No. 3, 0.004 c.c.; No. 4, 0.005 c.c., etc. If at the end 

 of the fourth day Nos. 1, 2, and 3 were dead and Nos. 4, 5, and 6 

 were alive we would consider the serum to contain 200 units of anti- 

 toxin for each cubic centimetre. When we mix only ten fatal doses 

 of toxin with one-tenth of the amount of antitoxin used with one hun- 

 dred fatal doses the guinea-pig must remain well. The mixed toxin 

 and antitoxin must remain together for fifteen minutes before injecting. 



Relation of Bacteriology to Diagnosis. We believe that all experienced 

 clinicians will agree that, when left to judge solely by the appearance 

 and symptoms of a case, there are certain mild exudative inflammations 

 of the throat which are at times excited by diphtheria bacilli and at 

 times by other bacteria. 



It is not meant to imply that a case is one of true diphtheria 

 simply because the diphtheria bacilli are present, but rather that the 

 doubtful cases not only have the diphtheria bacilli in the exudate, 

 but are capable of giving true characteristic diphtheria to others, 

 or later develop it characteristically themselves; and that those in 

 whose throats no diphtheria bacilli exists can under no condition give 

 true characteristic diphtheria to others, or develop it themselves 

 unless they receive a new infection. It is, indeed, true, as a rule, 

 that cases presenting the appearance of ordinary follicular tonsillitis 

 in adults are not due to the diphtheria bacillus. It is also true that 

 now and then a case having this appearance is one of diphtheria, and 

 almost every physician has seen such cases from time to time in house- 

 holds infected with diphtheria. On the other hand, in small children 



