THE AGGLUTINATION REACTION 301 



(3) Having made the mixture on the cover-glass, invert it over a 

 vaselined concave slide, label, and stand aside for an hour. 



(4) Prepare the culture control in the usual manner and label. 



(5) Examine at the end of an hour with the J/ or oil-immersion lens. 

 If minute fragments of fiber, etc., have been transferred, due allow- 

 ance for false agglutination for these should be made. Otherwise the 

 readings are made in exactly the same manner as in the "wet" method. 



(6) Accurate dilutions are not possible with this technic. Satisfac- 

 tory results are dependent largely upon the color; a faint orange tint 

 of the suspension is desirable, and probably represents a dilution of 

 about 1 : 40. This method, however, is very simple, and when care- 

 fully performed, yields results in the practical serum diagnosis of typhoid 

 fever almost as satisfactory as the serum-dilution method. 



It is possible, however, to work with known approximate dilutions 

 by the dried blood method if a good chemical balance is available. 

 Blood must be collected on aluminum foil or glass, and is then scraped 

 off and weighed. To each five milligrams of dried blood 0.5 c.c. of salt 

 solution is added which equals a dilution of 1 : 25 of whole blood or 

 1 : 100 of dried blood (Wesbrook). After permitting the mixture to 

 stand for half an hour it is centrifuged for a short time. To one drop of 

 the dilution thus obtained one drop of culture is added, which gives a 

 final dilution of about 1 : 50. At the end of an hour it is examined. 

 Higher dilutions can be prepared from this stock dilution at the will of 

 the operator. 



MACROSCOPIC AGGLUTINATION TEST 



This is frequently the method of choice in conducting agglutination 

 tests, especially in investigation and research work, where a high degree 

 of accuracy is desirable. All dilutions and measurements are to be made 

 with accurate volumetric pipets. 



1. Place a row of seven small test-tubes (10 x 1 cm.) in a test-tube 

 rack and add 1 c.c. of normal salt solution to each. 



2. Dilute the serum 1 : 5 in the first tube, as follows: 0.2 c.c. serum 

 plus 0.8 c.c. salt solution. This now gives in this tube 2 c.c. of a dilution 

 of 1 : 10. Mix well with the pipet. 



3. Place 1 c.c. of the serum from tube 1 into tube 2. Mix well, and 

 place 1 c.c. of the mixture from tube 2 into tube 3, and so on. When the 

 sixth tube has been reached, discard 1 c.c., as no serum is to be added to 

 the seventh tube, which is the culture control; i. e., it will contain salt 

 solution plus bacterial emulsion. 



4. Add 1 c.c. of bacterial emulsion to each tube, which doubles the 



