1911.] On the Factors Concerned in Agglutination. 425 



by the lysis of the red cells. For this reason a middle-piece solution 

 prepared from fresh guinea-pig serum was used in the majority of the 

 ■experiments. 



Addition of Middle-Piece to Sensitised Cells. 



The action of the solution of middle-piece can he demonstrated in a very 

 striking manner hy adding middle-piece solution to corpuscles previously 

 sensitised with the homologous antiserum. 



One cubic centimetre of a 1 in 20 suspension of sheep red cells was added to 

 1 c.e. of a 1 in 200 dilution of antiserum. The mixture was allowed to stand for 

 half-an-hour at room temperature. At the end of this time there was no 

 •evidence of agglutination. There was then added 1 c.c. of a 1 in 10 solution 

 ■of middle-piece. The red cells immediately ran together into large clumps 

 and rapidly settled to the bottom of the tube. This experiment showed that 

 the middle-piece solution could exert its action on already sensitised red 

 cells, and that it was not essential that the middle-piece should be present 

 from the time of the first admixture of antigen and antibody. The sensitised 

 red cells can, in fact, if freed by repeated washings from every trace of 

 uncombined antibody, be still agglutinated by the addition of middle-piece 

 solution. Previously sensitised red cells are, in fact, agglutinated with 

 great rapidity, for time is not taken up by the union of the red cells with the 

 antibody. 



Influence of Temperature on the Reaction. 

 No strictly comparative experiments have as yet been undertaken with a 

 view to ascertaining the influence of temperature on the agglutination of red 

 ■cells by immune body and middle-piece solution. The majority of experi- 

 ments were carried out at room temperature, but the agglutination was 

 somewhat accelerated by placing the tubes in an incubator at 37° C. On 

 the other hand, it was ascertained that a very marked degree of agglutination 

 was reached when the tubes were placed in the cold room at a temperature of 

 a few degrees above 0° C. The middle-piece solution is certainly able to 

 ■agglutinate sensitised corpuscles in the cold, and the delay in agglutination is 

 sufficiently explained by the longer time required at a low temperature for 

 the union of the red cells with antibody. 



Agglutination of Bacteria. 

 A considerable number of experiments were made with the object of 

 reproducing with bacterial emulsions the results obtained by the use of 

 blood corpuscles. In these experiments an inactivated antityphoid serum 

 •derived from a rabbit and an emulsion in normal saline of a 24-hours' agar 



