S14 



iKiAKD oi' Aci.Mi ii.rriM-; 



l"oll(t\V('(l liy fatal rt'snlis. only well cocked ami well ciiicil |i(irl< slioiild bo 

 calcii. It is impossilic {(H- tlic parasite to survive the i)ro]U'i' eookin^r or 

 iuriiiu of till' iiu'nt. 



Iiiumiiiity.- Tlu' sulijeet of iiiniiunity and imiimiiizat ion is of so nineli 

 intiTosl to swiuo hn-cders that the addition of a sjiecial aitielo setting 

 forth the basic jirinciplcs seems to l)e deniandod. 



Immunity is that jiower of resistance which every form of life pos- 

 sesses a.iiainst injury or (h'struction by some other form. The term is 

 used almost wholly in the sense of expressing a resistance of an individual 

 to dise.ise. It is an iidierent tiuality in all auimal or plant life. The resist- 

 ance in the different species toward the same cause and in individuals of 

 the same species to different causes. Th(> term is no longer ai)plie(l to the 

 resistance of tlie individual to some orjjjanism btit it is made to include the 

 products or toxines of the organism. Immunization is the process by 

 which the resistance may be increased toward any parti<ular form of 

 organism. 



The difference in imnumity in the different species toward the same 

 cause is easily illustrated by a comparison of the diseases occurring in the 

 human subject and in the lower animals. In the human we have, cholera, 

 typhoid, and yellow fever, th.nt are never found in other species. The 

 lower animals therefore possess a A'ory high degree of immunity toward 

 these diseases. In swine we have sAvine plague that never occurs in the 

 human. In cattle we have southern cattle fever that does not affect any 

 other species. We have other diseases as tuberculosis and glanders that 

 may affect the human and some of the lower forms. There are some dis- 

 eases of the human that have not been successfully inocnlated into the 

 lower animals and likewise diseases of one species that do not occiu* in 

 another. An individual or a species may have a very strong natural im- 

 munity to a given form but by exposure under adverse conditions r)r l)y 

 inoculation may become affected. Immunity is therefore only a relative 

 term and is not absolute. It is said to be strong or weak as nu'asured by 

 the degree of resistance under ordinary conditions. 



Age is an important factor in natural immunity. The young as n rule 

 offer a lesser degree of resistance to infectious di.seases than do the old, 

 AVhile the latter shows a greater susceptibility to chronic affections. This 

 can probably be best illustrated from examples in the human subject. 

 Children are prone to have measles, scarlet fever, chicken pox," "mumps" 

 and these are commonly known as children's diseases. A ])erson may 

 contract one of these diseases when they have arrived at maturity, but 

 the chances of doing so are very greatly reduced. This is often ascribed 

 to the fact that most i)ersons have these troubles avIkmi young and there- 

 fore are protected against a second attack. Tlie f.ict i-emains, however, 

 that among persons who have escai»ed these diseases wliile young the 

 power to resist an attack is greater than in the averagt? child. To draw 

 a like illustration from the lower animals we may cite the fact that sore 



