3l8 BACTERIOLOGY. 



susceptible animals immunity to the diseases 

 in question and therefore apparently acted 

 qualitatively or isopathically. Ehrlich showed 

 that the milk of immunized animals exerted 

 the same effect. Immunity obtained by the 

 use of the serum was somewhat transient as 

 compared with immunity acquired by means 

 of inoculation with the living parasites or their 

 metabolic products, and as compared with the 

 acquired habituation to poison : it lasted only 

 a short time, but on the other hand it made its 

 appearance very quickly. It was, so to speak, 

 " passive," while the other was " active." This 

 difference between active and passive immu- 

 nity, which apparently cannot be bridged over, 

 may be illustrated by the following examples : 

 If sheep are endowed with an active and 

 durable immunity against cutaneous anthrax, 

 they will nevertheless succumb to intestinal 

 anthrax, as Koch has proved. If rabbits are 

 inoculated with rabbit septicaemia in one ear or 

 On the cornea of one eye, a subsequent infection 

 on the same side of the body no longer takes 

 effect ; but, according to Loffler, the animals 

 still succumb to infection of the ear or cornea 

 on the other side, and it is only after some time 

 that a general immunity of the whole organism 

 can be remarked. According to Pasteur, rab- 

 bits which are protected against hydrophobia 



