26 CONSTITUENTS OF MILK 



6° C. for thirty minutes, whereas complement is destroyed by 

 this treatment; complement is, therefore, thermolabile. 



Antibodies, like enzymes, are of unknown chemical constitu- 

 tion and are usually designated by the natm-e of the action pro- 

 duced; thus, antitoxins neutraUse toxins, cytolysins dissolve 

 animal cells, hsemolysins dissolve erythrocytes, bacteriolysins 

 dissolve bacteria, agglutinins agglutinate cells and bacteria, and 

 precipitins produce precipitates from solutions. 



Immunity, by which is understood the existence of a cer- 

 tain resistance toward deleterious influences, may be either 

 acquired or natural. The apparent immunity of individuals, 

 races, and species to various diseases under normal conditions 

 is known as natural immunity, and very little is known of the 

 etiological factors involved. Acquired immunity may be acci- 

 dental, as in the case of the immunity acquired by an attack of a 

 disease, or artificially acquired by the introduction into the 

 system of either antigens or antibodies. When antibodies are 

 employed, the immunity is but of short duration compared 

 with the several years of immunity obtained by the use of anti- 

 gens. The former process is known as passive immunity and 

 the latter as active immunity. 



When antibodies are present in the blood, certain quantities 

 are excreted by the milk glands and may be foimd in the milk. 

 Ehrlich has demonstrated that offspring may, through suckling, 

 obtain a passive immunity from either an actively or passively 

 immunised mother. The antibody content of milk is usually 

 very much weaker than that of the blood from which it is 

 derived. Uniceptors of the second order are also transferable 

 to the milk and may be less than, equal to, or even greater, than 

 the amounts found in the blood. The evidence regarding the 

 transfer of the third order of antibodies is somewhat conflicting. 

 Amboceptors and complement derived from the blood may 

 appear in the milk, but this is unusual and various experi- 

 menters have stated that complement is not present in normal 

 ripe milk except in minute traces. In colostrum and milk 

 derived from udders affected with mastitis, however, both 



