420 



Mr. H. K. Dean. 



[Oct. ia> 



standing small flocculi are apparent. The precipitate is brought down with 

 a centrifuge and resuspended in ice-cold distilled water. This process of 

 washing the precipitate is repeated, and the precipitate is then dissolved in 

 cold 0"85 per cent, sodium choride solution. The experiments were 

 performed during the summer months, and it was found that, unless care 

 was taken to keep the original mixture and the suspension of precipitate as 

 cold as possible, it was very difficult to redissolve the precipitate in the 

 saline solution. The saline solution was used in such quantity that the 

 resulting middle-piece solution corresponded to a 1 in 10 dilution of fresh 

 guinea-pig serum. The supernatant fluid from which the precipitate had 

 been removed was, as a rule, quite clear, but was generally filtered through 

 filter paper to remove any trace of suspended particles. Sufficient sodium 

 chloride was then added to make it equal to a 0'85 per cent, sodium chloride 

 solution. The resulting solution which contained the end-piece fraction 

 corresponded to a 1 in 10 dilution of the fresh guinea-pig serum. 

 Preparation of Other Materials — 



The red corpuscles were obtained from the sheep. The blood was- 

 defibrinated with glass beads. The corpuscles were freed from serum by 

 three washings with normal saline solution. The hemolytic serum was 

 obtained from a rabbit which had had three intravenous injections of washed 

 sheep corpuscles. The serum was inactivated by heating for half an hour at 

 56° C. 



The bacterial emulsions were prepared by emulsifying in normal saline a 

 24-hours agar culture of B. typhosus. The antityphoid serum was obtained 

 from rabbits which had 'been immunised by intravenous injections of saline 

 emulsions of B. typhosus (killed by heating for one hour at 60° C). 



The antityphoid serum was inactivated by heating for half an hour at 

 56° C. 



Detailed Description of Experiments and Results. 

 Influence of the Middle-Piece on Agglutination — • 



An hemolytic serum, produced by injecting a rabbit with the washed red 

 corpuscles of a sheep, possesses, in addition to its haemolytic properties, con- 

 siderable power of producing agglutination. Agglutination of the red cells 

 is, however, evident only if a rather large amount of antiserum be present 

 in the mixture. In the case of the serum with which these experiments 

 was performed it was necessary to employ the serum in a strength of at least 

 1 in 100 to obtain any marked degree of agglutination within a period of 

 one hour. If the serum was employed in a dilution of 1 in 200 agglutina- 

 tion could not be detected. It may be mentioned that the hamiolytic titre 

 of this serum was about 1 in 1000. If to a mixture of one volume of a 



