IMMUNISATION AGAINST B. TYPHOSUS. 319 



on the matter. Many observers had noticed that the serum 

 of men convalescent from typhoid had an inimical effect on 

 typhoid bacilli ; and these results have been confirmed by 

 Pfeiffer, whose technique was less open to objection than 

 that of most previous workers. He found that the serum 

 of healthy men had such an action but in a much less 

 degree. The method was to mix the serum and the bacilli 

 in a little bouillon, and inject the whole intraperitoneally 

 into guinea-pigs. He found that when the latter did not 

 die, the bacilli became motionless and apparently dead, and 

 that plate cultures made after a time from the exudation 

 containing them, remained sterile. The serum of such 

 patients has, therefore, antimicrobic powers, but there is no 

 evidence that it contains any antitoxic bodies (see chapter 

 on Immunity). Pfeiffer, for example, found that on 

 adding serum from typhoid convalescents to the typhoid 

 toxines, and injecting the mixture into guinea-pigs, death 

 took place as in control animals which had received the 

 toxines alone. Sanarelli also found that while the injection 

 of toxines obtained as above described, rendered the animal 

 immune to a certain dose of living bacilli, it still could be 

 killed by a further dose of the toxine. He does not, how- 

 ever, give the doses employed. Pfeiffer found that by 

 using the serum of immunised goats he could, to a certain 

 extent, protect other animals against the subsequent injec- 

 tion of virulent living typhoid bacilli. On trying to use 

 the agent in a curative way, i.e., injecting it only after the 

 bacilli had begun to produce their effects, he got little or 

 no result. 



There is thus abundant evidence that the serum of 

 persons who have recovered from typhoid fever, and the 

 serum of animals artificially immunised against virulent 

 typhoid bacilli, protect from these bacilli. There is no 

 evidence that the serum has much power in neutralising the 

 products of these bacilli. We have thus this curious fact. 

 Animals are immunised by injections of the toxines of a 

 bacillus ; their serum, however, has no effect in neutral- 

 ising its toxines, but only aids in the destruction of the 



