518 IMMUNITY 



2. Immunity by Dead Cultures of Bacteria. In some cases 

 a high degree of immunity against infection by a given microbe 

 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 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 

 the power of which has been weakened by various methods (vide 

 infra). Afterwards the doses are gradually increased. This 

 method was carried out with a great degree of success in the 

 case of diphtheria, tetanus, malignant oedema, etc. It appears 

 capable of general application in the case of organisms where it 

 is possible to get an active toxin from the filtered cultures. It 

 has also been applied in the case of snake venoms by Calmette 

 and by Fraser, and a high degree of immunity has been 

 produced. 



The following may be mentioned as some of the most 

 important examples of the practical application of the principles 

 of active immunity, i.e. of protective inoculation : (1) Inocula- 

 tion of sheep and oxen against anthrax (Pasteur) (p. 346) ; (2) 

 Jenneriau vaccination against smallpox (p. 565) ; (3) Anti- 

 cholera inoculation (Haffkine) (p. 459) ; (4) Anti-plague 

 inoculation (Haffkine) (p. 486) ; (5) Anti-typhoid inoculation 

 (Wright and Semple) (p. 375) ; (6) Pasteur's method of inocula- 

 tion against hydrophobia, which involves essentially the same 

 principles (p. 579). 



Vaccines as a Method of Treatment. Up till recently the 



