Qualitative Tests 71 



The racks having been ordered, the solutions are viewed by trans- 

 mitted light to see if any are slightly cloudy. Where the cloudiness is 

 likely to obscure even a slight reaction the solution must be filtered or 

 discarded. The contents of the sealed tube containing antiserum 

 (Fig. 3 b) are now allowed to flow into a small test-tube such as is used 

 for testing; sediment in the sealed tube being excluded. By means 

 of a small tube of similar shape to that used in filling the solution into 

 the small test-tubes in the racks, the serum is now added in equal 

 quantity to all the solutions in the series. A drop or two suffices (equal 

 to "05 or even less of a c.c.)\ Where the antiserum does not flow down 

 to the bottom of the blood solution it is made to do so by gently tapping 

 the test-tube or by inserting a clean sealed capillary. On reaching the 

 end of the row, a slip bearing the name of the antiserum used, the time, 

 temperature, etc. is attached to the last rack in the row. In this way 

 a different antiserum is added to each row of bloods, until all have 

 received the test serum. The manipulation is exceedingly simple and 

 rapid, drops of antiserum of very uniform size being allowed to fall 

 from the pipette into each tube in the row. 



Where a powerful antiserum is added to its homologous blood 

 dilution, the reaction is almost instantaneous, in other cases it takes 

 place more slowly. In the case of a strong antiserum, the reaction 

 takes place as a rule rapidly in related bloods, more slowly in distantly 

 related bloods. The rate at which the reaction takes place may 

 depend also upon the concentration of the blood dilution, the more 

 concentrated dilutions, within limits, reacting earlier than higher 

 dilutions. A weak antiserum will act more slowly than a powerful one. 

 Consequently a " time limit" (Nuttall, 16, Xii. '01) may have to be put 

 on each antiserum when testing for a particular blood. In my earlier 

 tests I placed an arbitrary time limit of five to fifteen minutes upon 

 the reactions. Subsequently I lengthened the period of observation, 

 periodically noting the reactions which took place up to several hours, 

 indeed up to 24 hours at room temperature (varied between 12 and 

 20° C. in winter and summer), the deposits in the tubes being noted at 

 the end of the time mentioned. The black riband noted above, in 

 describing the stand, has proved of considerable value in studying the 

 slight reactions which are observable in more distantly related bloods, 

 or when testing more nearly related bloods by means of weak antisera, 

 where the reactions take place slowly and faintly. Many of the 



^ It is unnecessary to operate with larger quantities as other authors have done, as this 

 only entails a waste of antiserum. 



