GLOBULOCIDAL AND OTHER PROPERTIES OF SERUM 151 



the production of cytolysins. In fact, both cytolysis and agglutination may 

 occur at the same time. The normal blood serum of some animals may 

 be agglutinative for the blood-cells of some other species. In normal serum, 

 agglutinative and cytolytic properties may be present together or one only 

 may be normally present. 



The activity of agglutinative substances is not destroyed at a tempera- 

 ture of 56 C. They do become inert, however, at 70 C., and, furthermore, 

 they cannot be restored by adding normal serum, as is the case with cytolysins. 



Hemagglutinative substances are found in certain plant seeds; e.g., in 

 castor oil beans (Ricinus communis) , in cotton seed, and in the legumes. 



Precipitins. Other forms of adaptive substances which may be found 

 in animal serum are those which, when mixed with the substances by means 

 of which adaptation has been secured, form a precipitate. By this means 

 blood of different species of animals may be detected even when in a dried 

 state. It has been suggested as a possible valuable aid in medico-legal 

 cases, since human blood in a dilution of i to 50,000 has been recognized 

 by this means. 



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 Metchnikoff 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 



