

PRECIPITINS 227 



the culture medium by filtration, washed and suspended in normal saline 

 solution still retain the property of being agglutinated by a specific serum. 

 But, as Kraus and Ch. Nicolle have shown, if a culture be filtered through 

 porcelain a flocculent precipitate, similar to masses of agglutinated micro- 

 organisms, forms on the addition of a specific serum to the filtrate. It is 

 obvious therefore that the agglutinatible substance is also present in the 

 culture fluid ; it may be that as the organisms grow old the agglutinatible 

 substance passes into the culture fluid. The name precipitins has been 

 suggested for the substances in serum which cause the precipitate in filtered 

 cultures : there is evidence that precipitins and agglutinins are identical 

 bodies. 



Finally, certain chemical substances have the property of agglutinating 

 micro-organisms (Malvoz) but their action is in no way specific and the 

 same substance will agglutinate different micro-organisms (Beco). A mixture 

 of equal parts of commercial formalin, alcohol, hydrogen peroxide, a 1 in 

 1,000 solution of chrysoidin, vesuvin, safranin, or perchloride of mercury, etc., 

 agglutinates the typhoid bacillus as well as various other organisms. 



SECTION IV. BACTERICIDAL PROPERTIES. 



The fact that the serum of immunized animals has the power of destroying 

 bacteria was brought to light by one of Pfeiffer's experiments which has 

 since become classical. 



Pfeiffer's experiment. If a normal guinea-pig be inoculated in the peri- 

 toneal cavity with a broth culture of the cholera vibrio the animal rapidly 

 succumbs from peritonitis, and if the peritoneal exudate be examined micro- 

 scopically in a hanging-drop preparation it is found to contain very large 

 numbers of free motile vibrios, exactly similar to those inoculated. 



Let the same experiment be done on a guinea-pig which has been immunized 

 against the cholera vibrio ; the animal survives the inoculation and an 

 examination of the peritoneal fluid reveals an entirely different condition. 



In a drop of the fluid removed 10-30 minutes after the inoculation it will 

 be found that not only have the vibrios not multiplied but they have also 

 lost their motility, and instead of finding numerous elongated comma-shaped 

 organisms as in the former case, the fluid is seen to contain small granules 

 of no definite shape, which soon disappear altogether being destroyed in the 

 fluid in which they are suspended. 



This granular metamorphosis followed by complete destruction of the 

 vibrio may also be demonstrated in vitro (Bordet, Metchnikoff). 



Bordet's experiment. Break up a small quantity of an agar culture of the 

 cholera vibrio in a little sterile broth : examine the emulsion under a micro- 

 scope to see that there are no granular forms and that the vibrios are quite 

 motile : add to the emulsion ^V~TVth f its volume of the serum of an im- 

 munized guinea-pig. On examining the mixture a few minutes after the 

 addition of the serum, the vibrios will be seen to have lost their motility and 

 to have become agglutinated and converted into granular dots : the re- 

 action is however not at its maximum until the mixture has been kept at 

 37 C. for 1 or 2 hours. 



From these two experiments it may be concluded that the serum of 

 immunized guinea-pigs, apart from the intervention of any cellular element, 

 contains bactericidal and bacteriolytic substances capable of destroying the 

 cholera vibrio. 



These substances are specific so that the serum is only bactericidal for the 



