200 GENERAL BIOLOGY 



substances of the host. And these capsules only form in the body of a 

 host where some kind of immunity is possible. In cultures in the labora- 

 tory, where no immunity is brought into play, capsules do not form on 

 the groups mentioned. 



The encapsulated forms are not subject to phagocytic action, and 

 some even continue to produce more and more powerful poisons to in- 

 jure the unlucky phagocyte which may devour it. 



It is assumed that inflammations and fevers probably cause an in- 

 creased production of phagocytes and chemical neutralizations to pro- 

 tect the body in injury and disease. 



The amboceptors anchor soluble poisons only when the complement 

 is present. 



Similarly, phagocytes will not engulf bacteria unless the bacteria 

 have first been prepared for such engulfing by a substance in the normal 

 blood serum similar to the complement called opsonins. If an 

 animal has already been immunized by repeated introduction of bac- 

 teria, still more resistant bodies called bacteriotropins appear. These 

 bacteriotropins (which are only a sort of outstanding opsonin in immune 

 sera) act as opsonins and prepare the bacteria for the phagocytes. 

 Opsonins, bacteriotropins, and in fact all substances which prepare for- 

 eign substances for the phagocytes are called cytotropins. 



When foreign bodies of any kind dissolve body substances they arc 

 said to be cytolytic (cytes-cell-j-lysis-dissolving) if they dissolve the 

 cytoplasm ; haemolytic, if they dissolve the red substance (haema 

 blood) in the blood cell ; hepatolytic (hepar=Hver) if they dissolve liver 

 cells, etc., etc. Such lysins are usually antibodies. 



If a reaction can be produced which will cause bacteria or cells to 

 clump together, such clumping is called agglutination, while the sub- 

 stances in immune sera which cause agglutination are called agglutin- 

 ins. This is commonly called the Widal reaction. Agglutination is so 

 specific that the serum of an individual suffering from typhoid fever, or 

 even the serum of one who has had the disease, will cause the clumping 

 of typhoid bacilli when a few drops of it are placed in a culture of the 

 bacilli. 



If any foreign protein substance is injected into any of the higher 

 animals, new substances similar to antibodies are formed, which are also 

 specific in acting on the same protein substances by causing a cloudy 

 precipitate, and sometimes by changing the protein by breaking it up into 

 simpler substances, some of which are poisonous. This fact makes it 

 possible to tell whether blood stains are those of a human being or not. 

 For example, the clear serum of a rabbit can be treated with human 

 blood serum and if even a portion of the dissolved human blood stain is 

 then added, a cloudy precipitate forms, although this precipitate will 

 not form when blood from a lower animal is added. Similarly if the 



