154 



INFECTION AND IMMUNITY. 



Alexius. 



Natural 



Antitoxic 



Immunity. 



an important natural protective factor, and in 

 some instances it is the only one which can be 

 actually demonstrated, as in the case of staphylo- 

 cocci and streptococci. 



That organisms are often destroyed after being 

 ingested by the leucocytes is manifest from changes 

 in form which they undergo, and from the loss of 

 their staining power. Cultivation experiments 

 have also shown that the leucocytes are able to 

 kill certain bacteria. In such experiments, the 

 technic which was mentioned in testing the bac- 

 tericidal power of serum may be used, in this case, 

 however, substituting defibrinated blood, which 

 contains leucocytes, in place of the serum. If the 

 bactericidal power of the defibrinated blood is 

 greater than that of the serum alone, the effect of 

 the leucocytes becomes apparent. 



At a time when the antitoxic action of serums 

 was not appreciated, Buchner gave the name of 

 alexins (from the Greek, &\4fav 9 to ward off) to 

 the protective substances of the serum, i. e., to the 

 bactericidal substances, making the observation 

 that they were very labile substances, losing their 

 power spontaneously in a few days when exposed 

 to the air and light, or when they were heated at 

 55 C. for thirty minutes. As will be indicated 

 later, the "alexins" are more complex than Buchner 

 supposed. 



In determining the presence or absence of anti- 

 toxic immunity, the toxin of the microbe, of 

 course, must first be in hand. The methods of ob- 

 taining toxins will be referred to later. If the 

 animal resists a dose of toxin which, in proportion 

 to weight, produces disease in some other suscepti- 

 ble animal, the tissues or fluids of the first animal 



