I 7 PRACTICAL METHODS IN IMMUNITY 



live cultures are added with a pipette. Again, the dilution is unchanged by this 

 addition whereas it is doubled when an equal volume of culture is added to the 

 diluted serum. A control should always be made in normal salt solution. After in- 

 cubating, observe flocculent precipitates (agglutination) by tilting the fluid in the 

 tubes to form a thin layer and to obtain the most advantageous light and look for a 

 fine curdy precipitate (agglutination) or a uniformly turbid emulsion (negative 

 reaction). 



The method of using a slide with two vaselined rings, one containing 

 an emulsion in the specific serum and the other in salt solution is of 

 great practical value. This method is described under cholera. 



Pfaundler under the designation of a thread reaction showed that organisms 

 tended to grow in thread forms in a culture medium containing the homologous 

 serum. Mandelbaum has suggested this as a means of diagnosing typhoid. Take 

 ordinary bouillon containing i % of sodium citrate. Inoculate it with a culture of 

 typhoid. Now with a bulb capillary pipette take up i part (as marked by a wax 

 pencil) of the patient's blood and 15 times as much of the citrated bouillon just 

 inoculated with typhoid. Mix the blood and citrated bouillon on a sterile slide or in 

 a test-tube and after drawing up into the lower part of the expansion of the capillary 

 pipette, seal off the capillary end. Now place the sealed-off pipette upright in an 

 incubator and after four or five hours take out from the expanded end a loopf ul of the 

 clear supernatant fluid (the blood cells settle to the bottom) and if the typhoid bacilli 

 are in chains instead of being single and motile it shows a positive reaction. 



PRECIPITIN REACTIONS 



In the diagnosis of bacterial infections the agglutinating tests are 

 so much more satisfactory that precipitin tests are rarely applied. 

 As will be noted under the Meningococcus such a test has been recom- 

 mended for the diagnosis of cerebrospinal fever. 



In the technic of precipitin reactions for bacteria one filters two or three weeks 

 bouillon cultures of a given organism through a Berkefeld filter. (Precipitinogen.) 

 The filtrate should not only be perfectly transparent but also sterile as subsequent 

 bacterial growth would give turbidity similar to a positive reaction. The precipitin 

 containing serum is prepared by injecting rabbits intravenously with bacterial 

 filtrates as prepared above or with tne bacteria themselves. The methods are similar 

 to those for preparing agglutinating or haemolyzing sera. 



Test: To four tubes each containing 2 c.c. of the bacterial filtrate 

 are added increasing quantities of the serum to be tested; 0.05 c.c. to the 

 first tube, o.i c.c. to the second and 0.5 c.c. to the third, and i c.c. to the 

 fourth. Controls of positive and negative precipitating sera should 

 also be prepared. The tubes are not shaken and the reaction should 

 be allowed five or six hours at room temperature before final readings 



