SERO-THEBAPY 127 



The great amount of work that has already been done in 

 connection with the antitoxin treatment of diphtheria, 

 tetanus, erysipelas, typhoid, pneumonia, and plague, has 

 been the outcome of this line of research. 



The view that the condition of acquired immunity is 

 due to specific substances in the blood is not new ; but 

 what is new, however, is the experimental proof that such 

 ' anti-bodies ' do exist in the blood of an animal that has 

 been artificially immunised, as also in the blood of human 

 beings that have acquired immunity by having passed 

 previously through an attack of the disease. 



Many of the antitoxic sera possess a most marked 

 'specificity.' That is to say, although a given serum 

 has a most marked protective or curative action on cases 

 infected with the corresponding microbe, yet its immunising 

 action is not entirely confined to the one affection. Diph- 

 theria antitoxin has some protective action not only against 

 the diphtheria bacillus, but also against the bacillus of 

 typhoid and against streptococcic infection ; not only this, 

 but that a given animal, once immunised against one 

 organism, resists another species of organism far more 

 readily than a normal control animal. Starting with this 

 knowledge, several workers have for some time past been 

 engaged in increasing the natural resistance of a single 

 animal against more than a single infective process, and 

 strong hopes are expressed of eventually obtaining by this 

 means a serum of exalted immunising powers against each 

 of the original microbes. 



But Httle is at present known with respect to the 

 nature of the ' anti-bodies ' present in the blood serum of 

 immune animals, or of the means whereby they exer- 

 cise their property of neutralising toxins or bactericidal 

 powers. 



The chemical nature of these anti or protective bodies is 



