QUALITATIVE BACTERIOLOGICAL ANALYSIS. 185 



of agglutinating the B. typhosus. In doubtful cases I regard 

 this test of immunisation as a very important means of diagnosis 

 between the B. typhosus and varieties of B. coli. Fodor and 

 Rigler have shown that O'l c.c. and 0'5 c.c. of a typhoid broth 

 culture injected into a guinea-pig weighing 300 grammes 

 produce a serum with less agglutinating power than that 

 obtained when 1 c.c. is injected. They also believed from the 

 results of their experiments that increasing the amount of broth 

 culture to 5 c.c. per 300 gramme guinea-pig did not increase 

 the agglutinating power of the serum obtained, and that the 

 best results were derived from a serum taken from the animal 

 ten days after the subcutaneous injection of the broth culture. 

 These statements, however, did not hold good for the sera 

 prepared for me in the pathological laboratory at Netley. It 

 was always found that 3 c.c. of typhoid broth culture per 300 

 gramme guinea-pig produced a more powerful serum than 1 c.c. 

 of broth culture per 300 gramme guinea-pig. The whole question 

 of immunisation of experimental animals is very intricate ; much 

 depends on the health of the individual animal, it is very easy 

 to give too big an initial dose, and time must be given for the 

 animal to recover from the effects of the injection before pro- 

 ceeding to give another. By gradually increasing the dose, and 

 extending the injections over a period of three weeks, a more 

 powerful serum is usually obtained than when a single big dose 

 is given. Fodor and Rigler also believe that it is quite possible 

 for typhoid bacilli to become so altered that they will neither 

 become agglutinated by typhoid serum nor produce a serum 

 with agglutinating action ^hen injected into animals. In my 

 own experiments I have found that true typhoid bacilli may be 

 left in water and sewage for several weeks and still retain their 

 susceptibility to typhoid serum and the power of producing a 

 serum when injected into animals. 



THE RELATION OF TYPHOID BACILLI TO OTHER PATHOGENIC 

 AND NON-PATHOGENIC BACTERIA. 



Freudenreich has made some interesting experiments on this 

 subject. He inoculated flasks, containing 200 to 300 grammes 

 of broth, with different bacteria. After these had developed 

 the contents of the flasks were filtered through a Pasteur- 



