BACTERIAL POISONS. 165 



to heat. Most toxins become inactive at comparatively low temperatures 

 (60° to 70° C). 



Other physiological properties of the toxins will be brought out in connection 

 with the discussion of immunity. 



There is good reason on both chnical and experimental grounds to beUeve 

 that toxic substances are formed by the Micrococcus lanceolatus of pneumonia. 



In connection with bacterial poisons another class of bodies 

 may be conveniently described; these are agglutinins, lysins, 

 and precipitins. These bodies will be referred to again in 

 connection with antitoxin in the next chapter. 



Agglutinins. — The blood-serum of human beings as well 

 as of animals suffering from certain diseases has the power 

 of causing the bacteria of the disease from which the individual 

 has recovered to clump into larger or smaller masses in liquid 

 cultures to which the serum is added. The same phenomenon 

 is observed in the serum of animals injected with repeated 

 doses of cultures. This is due to certain substances called 

 agglutinins. The reaction, while it is more or less specific, 

 is not as strictly so as was formerly thought, for it has been 

 found that a given agglutinin may cause clumping of a group 

 of nearly related bacteria; such an agglutinin is called a group 

 agglutinin; and, moreover, under certain circumstances the bac- 

 teria fail to clump in the blood of patients suffering from a 

 given disease. Again, in some cases the serum in a certain 

 disease will clump bacteria that are not concerned in the 

 production of the disease. Even normal serum will some- 

 times clump bacteria. The serum from a given disease is 

 said to be homologous with the bacteria causing the disease 

 and heterologous from other bacteria, and the bacteria are said 

 to clump or not to clump with homologous sera, as the case 

 may be. Bacteria are also homologous or heterologous in 

 the same sense toward sera. 



Park* has recently found in this connection that homologous 



* W. H. Park. Proceedings of the New York Pathological Society. Vol. 

 IV., Nos. I and 2. February and March, 1905. 



