160 Dr. Wright and Capt. Douglas. Action on [July 26, 



first time overcome by Arloing, who obtained, by the operation of 

 a process of sejection, a strain of tubercle which gives a homogeneous 

 growth when the culture is frequently shaken up. For the homo- 

 geneous cultures of Arloing, Koch substituted a homogeneous sus- 

 pension of bacillary fragments obtained by the trituration of ordinary 

 tubercle cultures. Koch made his suspension with physiological salt 



solution. 



The test fluid thus constituted exhibits and this point did not 

 escape the observation of Koch a proneness to spontaneous agglutina- 

 tion. This defect, and it is a defect which may invalidate the results 

 of any test examination, can, as was pointed out by one of us,* be 

 eliminated by employing in lieu of the 0'85-per-cent. NaCl solution, 

 prescribed by Koch, a 0'1-per-cent. NaCl solution. f 



We have in the case of the investigations on agglutination which 

 are embodied in this paper in every case employed this 0'1-per-cent. 

 salt solution both for the dilution of the serum and for the suspension 

 of the tubercle powder. 



In some of our more recent experiments we have substituted for 

 the test fluid constituted as above a homogeneous suspension of tubercle 

 bacilli obtained by heating an ordinary tubercle culture to 60 C. for 

 an hour, filtering off the bacterial growth, breaking up this last in 

 a mortar with a solution of 0'1-per-cent. NaCl in 0'5-per-cent. carbolic 

 acid, and finally centrifugalising to remove any bacterial masses which 

 have not been resolved into their elements. 



In experiments conducted with either the one or the other of these 

 test fluids agglutination effects are obtained with normal human serum. 

 Conducting the experiments in throttled capillary tubes by the method 

 described by one of us,} and taking cognisance of the effect by 

 naked-eye inspection, a complete sedimentation is generally obtained in 

 the 2- and 4-fold dilution and incomplete sedimentation in the 8-fold 

 dilution. With some normal bloods complete sedimentation is 

 obtained up to the 16-fold dilution. 



Bactericidal Elements. Our investigations into the question as to the 

 presence of a bactericidal element in human serum are as yet in- 

 complete. 



Opsonins.As already brought out by us in previous papers, the 



* Wright ' Lancet,' July 25, 1903. 



f- The principle which suggested the replacement of the stronger by the weaker 



salt solution finds application, as one of us (S. E. D.) has recently elicited, also in 



the case of plague cultures. The spontaneous agglutination which has up to the 



resent been a source of difficulty in measuring the agglutination effect exerted 



a upon plague cultures can be completely avoided by employing a 0'1-per- 



it solution of salt in lieu of the broth or physiological salt solution ordinarily 

 employed. 



t Wright, loc. eft. 



' Roy. Soc. Proc.,' vols. 72 and 73. 



