200 General Biology 



a complement (or alexin), be present. These are protectors against 

 infection. 



Complements can be demonstrated to exist in the laboratory. When 

 blood serum is placed in a test tube, the receptors do not unite with the 

 toxin if a very small amount of heat is applied to the serum proper. 

 Heat kills or paralyzes whatever it is that makes the union possible. 

 If, however, we add but a very small amount of unheated serum, the 

 union takes place almost immediately. Whatever it is that has been 

 destroyed by the heating and permits or causes the receptor to unite 

 with the poisonous substance, is called the complement. 



It is quite possible that certain cells of the body, or even all the 

 cells of some animals, may have no receptors at all for certain poisons, 

 and, therefore, such cells and animals would have a natural immunity 

 toward those poisons. It is because the thrown-ofT receptor needs the 

 complement before it can anchor the poison that it has been called 

 amboceptor. 



The foreign body or substance is called the antigen, while the ambo- 

 ceptor produced by the action of injurious antigens is known as the 

 antibody. 



It is of great importance to know that the molecule which is the 

 amboceptor is decidedly specific. That is, an amboceptor will react only 

 to one specific foreign substance, so that antibodies formed in diphtheria, 

 for example, will not be the same as those formed in tetanus, nor will 

 they be able to assist in anchoring poisons produced in tetanus. 



Quite naturally, the rate and ability of metabolism in a cell will 

 determine how rapidly receptors are formed, and consequently will de- 

 termine how rapidly immunity can be brought about. This means, in 

 turn, that, if the poisons can act more rapidly than the cells, the cells 

 as well as the possessor of those cells will succumb. 



The growth, development and action of phagocytes (white blood 

 cells which devour foreign substances) are also subject to this same rate 

 and ability of metabolism. Some phagocytes may devour a foreign body 

 before the latter has time to bring about an injury. 



Some phagocytes may not have within themselves a chemical sub- 

 stance which can dissolve the invader, and so the invader may continue 

 to live even though engulfed by a phagocyte, or, the invader may even 

 kill the phagocyte. 



Then it must be remembered that in all parasitic organisms the 

 same conditions largely apply which apply in the host, so that, just as 

 the host may strengthen his resistance, so the parasite may strengthen 

 its virulence to overcome the increasing resistance of the host. For 

 example, about the bodies of the anthrax bacillus and the pneumococcus, 

 capsules form which make them more resistant to any injurious sub- 

 stances 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 



