TECHNIQUE OF BACTERICIDAL TEST-TUBE EXPERIMENTS. 349 



ill-suited for this purpose. One should, of course, never forget 

 to examine the normal serum for bactericidal powers previous to 

 immunization. 



With a great many bacteria it has not yet been possible to pro- 

 duce a serum bactericidal in vitro. Thus our experiments in this 

 direction extending over many years were unsuccessful with staphy- 

 lococcus pyogenes aureus (goat, rabbit) and with the diphtheria 

 bacillus. Nor have we been able thus far to obtain bactericidal 

 effects hi vitro from Susserin and other similar sera which are effective 

 in animal tests. The reasons for this behavior are not yet clear, 

 and they are therefore still being studied. 



Bordet and Gengou have devised a method (Annales de ITnstitut 

 Pasteur 1901) by the aid of which a bactericidal interbody pro- 

 duced by immunization can be recognized even in those cases in 

 which plate experiments fail (e.g. erysipelas of swine). This method 

 depends on the property, said to be possessed by bacteria to which 

 interbody has been supplied, of combining also with hsemolytic com- 

 plements. This loss of complement, which can be readily detected, 

 shows that the bacteria have combined with a bactericidal inter- 

 body. Without entering into the theoretical significance of this 

 interesting experiment we shall content ourselves by saying that 

 in several cases in which we tested bactericidal immune sera in this 

 way we failed to obtain satisfactory results. The method does not 

 seem to us to be suited to a quantitative estimation of an immune 

 serum. 



It need hardly be said that the first requisite for the success of 

 bactericidal experiments is that all vessels, diluting fluids, as well 

 as the sera employed be absolutely sterile. Great care is necessary, 

 especially in collecting the blood. The method described in the 

 preceding chapter for bleeding rabbits and guinea-pigs is sufficient 

 to obtain sterile blood. For collecting smaller quantities of blood 

 from the ear vein of rabbits it is necessary to first cleanse the ear 

 with 70% alcohol and then thrusting a short sterile hollow needle 

 into a vein. In many cases, to be sure, the blood can also be col- 

 lected by making a short incision across the marginal ear vein with 

 a sterile scalpel, and then, by holding the animal properly, allowing 

 the blood to flow out without running over the ear. 



In bleeding pigeons and chickens by decapitation one cannot 

 always count on sterile serum; hence it is well to lay bare the vessels 

 of the neck. For repeated bleeding of guinea-pigs one must also 



