520 Animal Biology 



certain diseases, etc. For example, if the blood serum of an animal im- 

 munized against typhoid organisms is mixed with a suspension of typhoid 

 organisms, the latter are agglutinated. The blood serum from a person 

 who has recovered from typhoid will likewise agglutinate typhoid organ- 

 isms but not other organisms even though they are closely related to 

 them. 



3. Precipitins^ which are antibodies with the power to precipitate 

 (settle out) foreign proteins against which they have been formed. After 

 precipitation the foreign proteins may be phagocytized in the body. Be- 

 cause precipitins are so specific, they are utilized in identifying specific 

 proteins of various organisms and in establishing the parentage of oflF- 

 spring in certain medicolegal cases. 



4. Bacteriolysins, which are antibodies which kill and dissolve the spe- 

 cific organisms which have stimulated the body cells to produce them. 

 Immune blood sera containing these specific antibodies are commonly 

 called antibacterial sera rather than antitoxin sera. 



5. Opsonins, meaning "to prepare food for," which are antibodies 

 which prepare bacteria so that they are more readily destroyed by the 

 phagocytes. The numerous opsonins are specific and act on only one 

 species of organism. The measurement of the opsonin content of blood 

 serum is known as the opsonic index. 



6. Antiaggressins — many bacteria secrete substances called aggressins 

 which repel or kill leucocytes. The body responds by forming an anti- 

 aggressin to neutralize the aggressin thus protecting the leucocytes. 



7. Complement and amboceptor — normal blood serum contains a sub- 

 stance called complement; immune serum contains other substances 

 called amboceptors, which are specific for the antigen which has stimu- 

 lated the body to form them. The two substances together aid in the 

 destruction of invading pathogenic bacteria. 



A phenomenon closely allied to antibody formation is known as hyper- 

 sensitivity, which is a state of a body which shows increased reaction to 

 a subsequent introduction of substances which provoked little or no 

 reaction when first introduced. Excessive and severe hypersensitivity in 

 animals and man is designated as anaphylaxis (meaning, "against pro- 

 tection," in contrast to prophylaxis which means "protection" or "pre- 

 vention"). Allergy (Fig. 256) ("altered reaction") is applied to milder 

 types of hypersensitivities in man. Some of the more common types 

 of allergies are ( 1 ) those due to inhaling such protein antigens as pollens 

 and dusts from animal hair, causing hay fevers, and certain types of 

 asthma, (2) those due to ingesting certain foods, such as milk, straw- 



