THE PROTECTIVE SUBSTANCES OF THE BLOOD. 379 



culties and did not succeed until the haemolysins were used in the 

 experiments in place of the bacteriolysins. 



Hsemolysins are peculiar poisons which destroy red blood-cells. 

 Such haemolysins are found in part in certain normal species of serum, 

 in part they can be produced artificially, as will be subsequently 

 described. In their fundamental properties they correspond entirely 

 to the bacteriolysins, but possess the great advantage over the latter 

 in that they readily permit the employment ot test-tube experiments 

 whereby the individual variability of the animal body is excluded, 

 and so allow accurate quantitative determinations. 



Belfanti and Carbone discovered the curious phenomenon that 

 the serum of horses, after they had been treated with blood-cells of 

 rabbits, contains substances which are highly toxic to rabbits, and 

 only to these animals. Bordet showed that the cause of this toxicity 

 is a specific hsemolysin directed againt the rabbit blood-cells. He 

 showed further that such hsemolysins, derived by injection of foreign 

 blood-cells, lose their power to dissolve blood when heated for half 

 an hour to 55 C. Bordet found also that the hsemolytic property of 

 such inactivated sera is again restored if certain normal sera are 

 added. These important observations showed a complete analogy 

 between these phenomena and those observed with bacteriolysins by 

 Pfeiffer, Metchnikoff , and especially by Bordet. In the case of bacteri- 

 olysins it was found that serum freshly drawn from a goat immunized 

 against cholera is able to effect solution of cholera vibrios, i.e., to give 

 the so-called Pfeiffer reaction. Apparently this property disappears 

 spontaneously if the serum is allowed to stand; it disappears rapidly 

 when the serum is heated to 55 C. The cholera serum rendered 

 inert by heating exerts its protective power in the animal body un- 

 changed; and in test-tube experiments it attains its original solvent 

 power on the addition of small amounts of normal goat or guinea- 

 pig serum, although the latter do not by themselves injure cholera 

 vibrios. 



These experiments show that in bacteriolysis two substances act 

 together; one, contained in immune blood, is relatively stable and 

 represents the carrier of the specific protective action; the other, pres- 

 ent in every normal serum, is easily destroyed. For the present 

 the former is called the "immune body," while the latter, since 

 it complements the action of the immune body, is called the "com 

 plement." 



Since the haemolysins are by far the most convenient for experi 



