NATURE OF THE ANTISUBSTANCES IN BLOOD 147 



Opsonins. Wright and Douglass have shown that there are certain 

 substances in the serum that affect bacteria in such a way that they are more 

 easily taken up and destroyed by leucocytes. The phagocytic power of the 

 leucocytes in destroying toxic bacteria is not made to increase by stimulative 

 substances, as Metchknikoff believed, but rather by those materials in the 

 serum diminishing the resisting power of the bacteria. These substances 

 are called by their discoverers opsonins. They found opsonin present in 

 normal serum, but also found that its quantity varies under certain conditions. 

 They suggested that the opsonins could be measured by determining the 

 phagocytic power. The ratio of the average number of bacteria taken up by 

 leucocytes in normal serum to the number taken up in the immune serum, 

 they called the opsonic index. 



Antitoxins. Certain kinds of bacteria, notably the diphtheria and 

 tetanus organisms, elaborate poisonous substances known as toxins. The 

 pathological conditions resulting from such infections are produced by the 

 poisons so formed. Behring first showed that immunity to diphtheria was 

 due to the presence in the blood plasma and blood serum of substances which 

 apparently combine with and so prevent the toxic action of the bacterial 

 products. This antitoxic power of the blood can be artificially developed by 

 injecting small doses of the toxins into an animal, usually a horse, at inter- 

 vals of some days. The protective power of the blood against the toxins can 

 thus be developed to a relatively enormous degree. The serum of an arti- 

 ficially immunized animal can be injected into other individuals of the same 

 or other species and an immunity will be conferred on the person or animal 

 so treated. Similarly, the antitoxic sera have a curative effect in infected 

 individuals if the disease is not too far advanced. Antitoxic sera are specific 

 for the particular toxin used for the immunization. Antitoxins can be 

 similarly prepared for the naturally occurring vegetable toxins, ricin and 

 abrin, for snake venoms, etc. 



Anaphylaxis. It has been found that if an animal, especially the 

 guinea pig, be injected with even the minutest quantity of protein material, 

 that after ten to fourteen days, the animal becomes susceptible to a sec- 

 ond injection of the same material if made intravascularly. Thus a guinea 

 pig may be sensitized with o.oooooi of a c.c. of blood serum; after two 

 weeks have elapsed, the introduction of a half c.c. of the same serum into 

 the circulation will in a few minutes lead to respiratory failure and death. 

 This phenomenon is relatively specific for foreign protein substances. 

 Guinea-pigs which have recovered from the second injection acquire a 

 temporary immunity against a third injection of the same protein. It has 

 been found that this peculiar susceptibility is transferred from the mother 

 guinea-pig to successive litters. 



Nature of the Antisubstances in Blood. The lecithins and fatty acids, 

 especially oleic acid, will in a measure replace a hemolytic complement. 



