.126 CLINICAL BACTERIOLOGY AND H^EMATOLOGY 



far too weak. None is fit to use that does not contain 2\ 

 haemolytic doses, i.e., that will not give with normal serum 

 complete haemolysis under standard conditions when diluted 

 2| times. To test it, prepare a series of i to 4 dilutions in 

 normal saline of several samples of sera from healthy per- 

 sons. To each add a mixture of i part of emulsion of cor- 

 puscles and i part of amboceptor : stir after five minutes and 

 read off the result in another five. There should be complete 

 haemolysis in all. Repeat with amboceptor diluted i in 2 and 

 i in 3. If there is complete haemolysis in i in 2, and partial 

 in i in 3, the amboceptor is of sufficient strength for use. If 

 there is complete haemolysis in i in 3, it should be tested higher 

 and diluted for use as the results suggest: thus if it gives 

 complete haemolysis when diluted five times, it may be 

 diluted with an equal amount of saline for use, giving 2.\ 

 haemolytic doses. (Greater accuracy is given by estimating 

 the amount of complement in each specimen of serum and 

 diluting it accordingly; but this is unnecessary for practical 

 purposes if several specimens of normal serum, say half a 

 dozen, are used in the process.) 



Apparatus. I greatly prefer the special incubator that 

 Messrs. Hearson have made for me, as the tubes stand in a 

 water-bath, and so are brought almost instantaneously to the 

 requisite temperature (see Fig. 25). A similar tray is inserted 

 in the incubator referred to on p. 20. The test can be carried 

 out quite well in an ordinary incubator, but the incubation 

 must be longer (ten to fifteen minutes). If this is done, it is 

 convenient to stick the tubes side by side on a slip of wood 

 or a box-lid covered with plasticene, a substance that is of 

 use in a variety of ways in the pathological laboratory. 



The test-tubes should be about J inch in internal diameter 

 and 2 inches long. They can be procured or easily prepared 

 from suitable glass tubing. 



The only other piece of apparatus is a pipette, such as is 

 used for opsonic work, the Widal reaction, etc. It should 

 not be too wide (so as to avoid waste of material), and a unit 

 mark should be made about J inch from the tip. Then take 

 4 of these units of water or other fluid, expel them into a 

 watch-glass, and suck the 4 into the pipette so as to form a 

 continuous column. Make a mark to indicate the point to 

 which this column reaches and you will have a pipette which 



