THE RELATION OF LIPOIDS TO IMMUNITY 557 



To 10 c.c. of the colloidal gold in a clean beaker add 2 drops of 

 indicator. If it is acid, titrate to the neutral point with -^ NaOH; if 

 alkaline, with f$ Hcl. Calculate the amount to be added for the amount 

 of colloidal gold solution at hand and neutralize with normal or deci- 

 normal solutions of acid or alkali as required. 



The following are suitable standards for a good colloidal gold 

 product: 



(a) Absolutely transparent and of a brilliant red orange or salmon- 

 red color. 



(6) Five c.c. of the solution must be completely precipitated in one 

 hour by 1.7 c.c. of a 1 per cent, solution of sodium chlorid in distilled 

 water. 



(c) The solution must be neutral in reaction when used. 



(d) The solution must not produce a reaction greater than a No. 1 

 with normal cerebrospinal fluid, and must give a typical reaction curve 

 with a known pare tic fluid. 



The Test. 1. Arrange eleven clean, dry test-tubes in a row; put 

 1.8 c.c. of fresh, sterile 0.4 per cent. NaCl solution into the first tube 

 and 1 c.c. in the following ten. 



2. With a clean, dry pipet add 0.2 c.c. of a blood-free cerebrospinal 

 fluid to the first tube and mix; transfer 1 c.c. from the first to the second 

 tube, mix, and proceed in this manner up to and including the tenth tube, 

 from which 1 c.c. is discarded. The eleventh tube is the control and 

 contains no cerebrospinal fluid. The dilutions now range from 1 to 10 

 to 1 to 5120. 



3. Add to each tube 5 c.c. of colloidal gold; mix and stand aside at 

 room temperature over night; the readings are made the next day 

 and recorded by numbers according to the following scheme: 



5 = complete precipitation (water clear). 



4 = pale blue. 



3 = blue. 



2 = lilac or purple. 



1 = red-blue. 



= no change. 



Types of Reactions. 1. Normal fluid produces no changes at all 

 or, at most, a No. 1 change in the first tube of the series. 



2. The typical reaction is observed in general paresis, giving com- 

 plete precipitation in the first four to eight tubes of the series, with 

 changes of color in most of the remaining ones, as, for example, 

 5555542100, and constituting the "paretic curve" of Miller and 



