338 TYPHOID FEVER. 



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, antibacterial 

 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 bodies 

 of typhoid bacilli killed by heat, and injecting the mixture into 

 guinea-pigs, death took place as in control animals which had 

 received these toxic agents alone. Sanarelli also found that 

 while the injection of similar toxic fluids rendered the animal 

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

 by a further dose of the toxin. Pfeiffer found that by using the 

 serum of immunised goats he could, to a certain extent, protect 

 other animals against the subsequent injection 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 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 intracellular toxins of these bacilli. We 

 have thus this very important fact. Animals are immunised by 

 injections of the toxins of a bacillus ; their serum, however, has 

 no effect in neutralising its toxins, but only aids in the destruc- 

 tion of the bacilli which produce the toxins. Similar results 

 have been obtained in the case of cholera. 



The Pathogenicity of the B. coli and its Relation to that of the Typhoid 

 Bacillus. — We have already seen that the B. coli is probably responsible for 

 the occurrence of some of the abscesses which follow typhoid fever. It is 

 also apparently the cause of some cases of summer diarrhoea (cholera nostras), 

 and of infantile diarrhoea. Its numbers in the intestine are greatly increased 

 during typhoid fever, and also during any pathological condition affecting 

 the intestine. Intraperitoneal injection in guinea-pigs is occasionally fatal. 

 Subcutaneous injection results in local abscesses, and sometimes in death 

 from cachexia. Sanarelli found that the B. coli isolated from typhoid stools 

 was much more virulent than when isolated from the stools of healthy 

 persons. He holds that the increase in virulence is due to the effect of the 

 typhoid toxins, and devised an ingenious experiment which seems to prove 

 this point. This increased virulence of the B. coli in the typhoid intestine 

 makes it possible that some of the pathological changes in typhoid may be due, 

 not to the typhoid bacilli;^ , but to the B. coli. Some of the general symptoms 



