17 231 



are found tobe only */2, V2 and Va, respectively, of that of the unhealed serum. Yet 

 in spite of this, "zones of inhibited agglutination" are a far more prominent feature 

 witli the agar-culture suspensions than they are with the bouillon-cultures of B. coli. 



Continuing with these experiments, it is seen that prolonged heating to 70° 

 causes this increased agglutinating power, seen only when agar-culture suspensions are 

 used, to disappear again. Thus the serum diluted 1 : 10 became twice as strongly 

 agglutinating after being heated at 70° for half-an-liour ; but after 2 hours at 70° it 

 was only a little stronger than it was before being heated; it must be emphasised 

 that these measurements were made on the agar-culture suspension of B. coli. The 

 experimental results detailed in Series 59 to 68 shew that within certain limits the 

 greater the dilution at which the heating is performed, the greater is the reduction of 

 the serum's agglutinating power, whether bouillon-culture or agar-culture suspension 

 be employed — though the fact is best illustrated when the former is used. To 

 quote an example, if the agglutinating immune-serum in the three dilutions 1 in 10, 

 1 in 100, and 1 in 1000 be heated to 70° for 1 hour, and the agglutinating powers of 

 the three dilutions be then measured on a 24-hour bouillon-culture of B. coli, they 

 will be found to have fallen to V2, ^U and Va of their original values — see 

 Series 68. If, on the other hand, an agar-culture suspension be employed, the 

 results, as is shewn by the figures in Series 67, are quite different. The agglutinating 

 power of the 1 in 10 dilution is twice what it was before, while the 1 in 100 

 dilution is a little weaker (in the proportion 1 to 1'3), and the 1 in 1000 dilution 

 has only one half of the agglutinating power it had before the heating. 



It results from all these sets of experiments that the weakening of the agglut- 

 inating power of the B. coli serum is much more apparent when the measurements 

 are made using bouillon-culture, than when an agar-culture suspension is employed. 



At the present moment it is impossible to say which of the two sets of results 

 mentioned above should be regarded as giving the more correct view of the effect 

 of heat upon agglutinating immune-sera. Further observations with other varieties 

 of serum are needed before that question can be decided; and such experiments 

 as are now in progress have not advanced sufficiently far to permit definite con- 

 clusions to be drawn. 



The figures quoted in Series 67 and 68 further shew that if the dilutions of the 

 agglutinating immune-serum be made with 1 "/o normal horse-serum instead of with 

 normal saline, the loss of agglutinating power on heating to 70° will be greater. 

 This fact is particularly striking when bouillon-culture is used in making the 

 measurements, when, also, a "zone of inhibition" occurs which is, however, small 

 in extent, and diminishes if the test-tubes are allowed to stand and are observed 

 again after the lapse of many hours. 



The occurrence of these "zones of inhibited agglutination" is explained by Eisen- 

 berg & Volk as due to the conversion of a part of the agglutinine into agglutinoid 



I). K. 1). Viilensk. Selsk. Ski-, 7. Ita-Ukc, iialiiiviileiisk. o« miithein Am 1. 4 31 



