168 A MANUAL OF BACTERIOLOGY 



fraction. It is thus possible to concentrate antitoxic serum and to 

 make use of a weak serum, which would otherwise be inconvenient 

 on account of the volume necessary to inject in order to introduce 

 the requisite amount of antitoxin. For this purpose various salts 

 have been employed for saturation, ammonium sulphate (Pick and 

 others), magnesium sulphate (Dieudonne), mixtures of sodium and 

 potassium chlorides (Atkinson), etc. 



Dzergowski and Predtechensky l have elaborated a very exact 

 method by which they state that the whole of the antitoxin can be 

 concentrated and recovered from a comparatively weak serum by 

 means of precipitation with ammonium sulphate. 



ANAPHYLAXIS. An animal usually becomes more and 

 more tolerant to injections of an antigen, e.g. to diphtheria 

 and tetanus toxins in the preparation of the corresponding 

 antitoxins. Sometimes, however, the opposite effect is 

 produced, viz. increased sensitiveness. This has been 

 noticed in the preparation of tetanus antitoxin ; after 

 the animal has received a few doses of the toxin without 

 ill-effect, a smaller dose of toxin may cause fatal tetanus. 

 The tuberculin reaction is, probably, another example ; 

 tubercle toxins circulating in the tuberculous individual 

 render him peculiarly sensitive to a minute dose of tuber- 

 culin (i.e. tubercle toxin) which in a normal person produces 

 no effect. Sensitisation may be obtained with difficulty 

 by administration by the mouth, and this may be the 

 explanation of the urticaria, etc., produced in some indi- 

 viduals by certain foods, e.g. shell-fish. This condition of 

 hypersensitiveness is known as " anaphylaxis " (i.e. the 

 opposite of " prophylaxis "). Probably any antigen under 

 particular conditions may induce anaphylaxis, but the 

 phenomenon has been especially studied in connexion with 

 serum injections, though any protein, e.g. egg-white or 

 bacterial cells, similarly causes it. The injection of an 

 anti- serum usually produces no ill- effect other than the 

 rashes, joint pains, and pyrexia already mentioned, even 



1 .See Hewlett's Serum Therapy, 1910, p. 68. 



