BY BACTERIAL PRODUCTS OR TOXINS 555 



may be developed by repeated and gradually increasing doses 

 of the dead cultures, the cultures being killed sometimes by 

 heat, sometimes by exposure to the vapour of chloroform. In 

 this method the so-called endotoxins will be injected along with 

 the other substances in the bacterial protoplasm, but the result- 

 ing immunity is chiefly directed against the vital activity of the 

 organisms is antibacterial rather than antitoxic (vide infra}. 

 The cultures when dead produce, of course, less effect than when 

 living, and this method may be conveniently used in the initial 

 stages of active immunisation, to be afterwards followed by 

 injections of the living cultures. The method is extensively 

 used for experimental purposes, and is that adopted in anti-plague 

 and anti-typhoid inoculations, and in the treatment of infections 

 by means of vaccines. 



3. Immunity by Sensitised Dead Cultures. In this method, 

 which was originally introduced by Besredka, the bacterial 

 emulsion is treated with the corresponding anti-serum, that is, 

 the serum of an animal immunised against the particular 

 bacterium, and after being left in contact for some time, the 

 serum is separated by the centrifuge and the bacteria are 

 thoroughly washed free of all traces of serum. The bacteria 

 thus treated constitute the vaccins sensibilises. It is claimed 

 that, while immunity produced by them is rapidly developed 

 and is of long duration, the local toxic effects on subcutaneous 

 injection are very much lessened. The method has been applied 

 in vaccination against typhoid, plague, cholera, and dysentery. 

 Apparently in such sensitised vaccines the antigen molecules of 

 the bacteria will be largely combined with anti-substances, and 

 thus on theoretical grounds we would expect that only those 

 molecules left free, or those which become free by dissociation, 

 will be able to act as antigens and the antigenic power of the 

 bacteria will be diminished. Certain observations show that this 

 is the case, but it would be desirable to have fuller knowledge of 

 the amounts of anti-substances developed by the sensitised and 

 non-sensitised bacteria respectively and of the relation of such 

 amounts to the degree of protection afforded. 



4. Immunity by the Separated Bacterial Products or 

 Toxins. The organisms in a virulent condition are grown in 

 a fluid medium for a certain time, and the fluid is then filtered 

 through a Chamberland or other porcelain filter. The filtrate 

 contains the toxins, and it may be used unaltered, or may be 

 reduced in bulk by evaporation, or may be evaporated to dryness. 

 The process of immunisation by the toxin is started by small 

 non-lethal doses of the strong toxin, or by larger doses of toxin 



