60 BACTERIOLOGY FOR NURSES 



jaZexmes^and the de gree of immnnity was dependent 

 u pon the _a mount of a le xines contained in th e blood; , 

 but it has been found that in some cases there is no 

 relation between the resistance of the animal and the 

 bactericidal power of its blood-serum. The human 

 blood-serum is strongly bactericidal for the bacillus 

 of typhoid fever, but that fact does not always pre- 

 vent the multiplication of the organism in the blood 

 during an attack of the disease. The chief difference 

 between an antitoxic serum and a serum which is 

 bactericidal is, that an antitoxin acts only upon a 

 formed poison, while a bactericidal serum may be 

 protective, preventing an infection. The antitoxin 

 of diphtheria affords the best example of an antitoxic 

 serum; it not only neutrahzes the diphtheria toxin, 

 but is also curative. 



Certain bactericidal sera which are bacteriolytic 

 (dissolving) in their action have been used only in a 

 limited degree in the diseases of man, as they can only 

 be artificially cultivated in the lower animals and 

 have not always proved satisfactory, because of the 

 differences in . species, it is supposed. The blood- 

 serum from animals inoculated with typhoid bacilli 

 has been found entirely ineffective when used for 

 treating the disease in man; and on the other hand, 

 the use of the bacterial cells by vaccination as a 



