xxi] PATHOGENIC ORGANISMS 575 



figure of about 90, 130, and even 200 units, or, more 

 accurately stated, 7'5 cc. of serum possess 600, 1,000, or 

 1,500 antitoxic units respectively. Roux submits horses — 

 as a rule not possessed of great susceptibility for diphtheria at 

 the outset — to repeated injections with pure and powerful 

 diphtheria toxin, starting by injecting subcutaneously small 

 doses of attenuated toxin, then gradually increasing the 

 dose of the pure toxin, till after many injections the intra- 

 vascular injection of enormous doses — 250 cc. — of the 

 most powerful toxin do not produce more than a transitory 

 result. After three months' immunisation he obtains an 

 antitoxic serum which is possessed of great potency : one 

 cubic centimetre being capable of neutralising a fatal dose 

 of pure toxin for 10,000, 20,000, 50,000, 100,000 and even 

 200,000 grams guinea-pig, or, put differently, -g\, -j-^, ^to, 

 -g^jj, and even y^-j-^ of a cubic centimetre of the antitoxic 

 serum can completely neutralise the effect of a fatal dose of 

 toxin injected into a guinea-pig of 200 grams weight. But 

 while this serum possesses the high antitoxic power, i.e. the 

 neutralising power of toxin, both when injected into the 

 unprepared animal shortly before or simultaneously with, 

 or some hours — six or even twelve hours — after the toxin, 

 its germicidal potency, i.e. its action against the living 

 microbes (Diphtheria bacilU), is considerably less, though 

 it is for a time at least considerable. Thus, for instance, of 

 Behring's diphtheria antitoxic, serum, marked 600 units, j\,- 

 of a cubic centimetre is required to completely neutralise 

 for a guinea-pig of 500 grams weight a fatal dose of living 

 culture of the diphtheria bacilli, ^^ of a cc. does not pre- 

 vent the formation of a tumour, although the animal does 

 not die, but recovers after some days, jjjjy of a cc. neither 

 prevents the formation of a tumour nor the fatal issue. 

 I have succeeded in obtaining serum of considerable anti- 



