172 Dreyer and Douglas. Velocity of Reaction in [Nov, 16, 



it is possible to express the agglutinin strength of the serum in arbitrary 

 units. Thus it will be seen that it is possible to measure the agglutinin 

 content of a given serum, whether it is strong or weak, with the same 

 procentic accuracy, i.e. to determine whether a serum contains 1 or 1*1 unit 

 as accurately as if it contained 1000 or 1100 units. 



The digesting power of the trypsin used in one set of experiments was 

 measured in a similar manner. A slightly alkaline 10 per cent, gelatin jelly, 

 to which had been added a trace of thymol, took the place of the bacterial 

 culture, the trypsin solution that of the diluted serum. After the fluid 

 contents had been measured into the tubes, these were shaken and placed in 

 a water bath at 37° C. for two hours and then placed in a cold water bath 

 (8° to 10° C.) to solidify, and read while still in the bath. A second reading 

 was taken 24 hours later to make sure that the end reaction had actually 

 been reached. A tube which showed semi-liquefaction was chosen as 

 standard in reading the result. 



As we, in the course of our investigations, have been convinced of the 

 importance of paying attention to points previously raised by Dreyer and 

 Jex-Blake, it may be of use to summarise the principal differences between the 

 method as used by us throughout our experiments, and the method as 

 originally proposed by Madsen and Jorgensen. 



1. To use a standardised killed bouillon culture as described by Dreyer* 

 instead of a fresh 24-hour bouillon culture, of non-standardised strength, to 

 which 0"02 per cent, of formalin had been added immediately before use in 

 order to prevent the further growth of the bacteria while the tul)es were kept 

 for two hours at 37° C. 



2. To make the contents of each tube up to the same volume. Madsen and 

 Jorgensen, and also Jorgensen, have stated that variations in the same 

 amounts of fluid in their test-tubes lying between r56 c.c. and 2 c.c. made no 

 difference in the results they obtained, any alterations due to such variations 

 lying within the limits of experimental error. Our own experience, however, 

 is entirely opposed to this view. 



3. To take two separate readings of the tubes : the lirst after they have 

 been left two hours at 37° C. and allowed to cool to room temperature, and 

 the second after tliey have been loft a further 20 to 24 lioui's at room 

 temperature. This is preferable to the reading of tlu; tubes as soon as they 

 are removed from the water l)alh and before they have liad tinu; to cool down 

 to the tcrMperature of the room as proposed by Madsen and Jorgensen, a 

 course which is impossible wliere many series of tubes have to be examined, 

 and also, in our cxjtci icnce, gives less tiustworthy results. We (liid that tlie 



* ' IIoHi)ital8ti(lcn(le,' No. 1!), 1000, juid Mdiiiii. (if.I';itli. and l!;ut.,' vol. 1, 100<J. 



