25 239 



These facts cannot be properly appreciated nntil the ability of the HCl to 

 produce agglutination when it is acting alone has been measured. 



Series 81 shews that in this particular agar-suspension, agglutination as strong 

 as or even stronger than that in the standard tube was produced by quantities of from 

 0146 to 0026 mgrm. of HCL 



Hence the apparent increase in the agglutinating power of the serum depends 

 upon the presence of these small amounts of acid (from 0029 to 0026 mgrm.) which 

 are capable of producing the agglutination by themselves alone; and the experiments 

 just recorded prove that the agglutinating action of these small quantities of acid 

 is not prevented by the particular amounts of immune-serum that are being con- 

 sidered here. So much then for the lower Hmit of the "zone". 



For the position of its upper limit, at which it comes to an end, very similar 

 considerations hold good. The tubes that are agglutinated to the same extent in 

 the different series are found to contain nearly the same (or the calculated) amount 

 of acid, quite independently of the amount of acid with which the sera were 

 treated, or of the quantity of serum present in these tubes. The experiments in 

 Series 81, 84, and 88 bring this out clearly. One cannot help a feeling of surprize 

 that the quantities observed should tally so closely with those calculated, for the 

 upper limit of the zone as well as for the lower. 



It will also be noticed that when the measurements are made in an agar-culture 

 suspension, the extent of the inhibition zone produced by the acidified serum does not, 

 within wide limits, vary niith the amount of acid with which the serum was treated, 

 but depends solely upon the amount of acid present in the quantity of acidified serum 

 placed in the given tubes; this can be seen by reference to Series 82. 



The figures given in Table XXXII, Series 90, illustrate the fact that a precisely 

 similar explanation may be given of the "zone of inhibition" observed when an 

 emulsion of B. typhosus, derived from our stock culture, is exposed to the action 

 of acidified B. typhosus immune-serum. 



Thus we are unable to accept the explanation of the phenomena here described 

 that has been given by other experimenters. 



Our own view of the diminished agglutinating power and of the "zones of 

 inhibited agglutination" met with in the acidified sera is that both are mainly if 

 not entirely due to diminution in the velocity of the reaction; this diminution being 

 caused by the presence, in certain proportions, of the acid. The apparent increase 

 in the agglutinating power of the serum is due solely to the power possessed by 

 the acid of agglutinating per se when it is present in sufficient quantity. 



Inspection of the figures set down in Tables XXX and XXXI, Series 88 and 89, 

 brings out the fact that there are striking differences between the two readings 

 obtained, the one immediately after the tubes have been in the waterbath at 37° 

 for 1' 5 hours, the other after they have stood for a further 18 hours at the tem- 

 perature of the room. The extent of the "inhiliition-zone" is much diminished in 



1). K I). Viclensk. Selsk. Ski-. 7 H;i-kke. iiuUnvicl.Misk- OB ni;ithi-m- Al'.l ] J. 32 



