368 TYPHOID FEVEK 



of subcutaneous or intraperitoneal infection are no more satis- 

 factory. Here /pathogenic effects can easily be produced by 

 the typhoid bacillus, but these effects are of the nature of a 

 short acute illness characterised by pyrexia, rapid loss of weight, 

 inability to take food, and frequently ending fatally in from 

 twenty-four to forty-eight hours. The type of disease is thus 

 very different from what occurs naturally in man. In such 

 injection experiments the results vary considerably — no doubt 

 due to the fact that different strains of the bacillus vary much 

 in virulence. Ordinary laboratory cultures are often almost 

 non-pathogenic. They can, however, be made virulent in various 

 ways (see Chap. XXII.). 



The Toxic Products of the Typhoid Bacillus. — Here very 

 little light has been thrown on the pathology of the disease. 

 There exist in the bodies of typhoid bacilli toxic substances which 

 in artificial cultures do not pass to any great degree out into the 

 surrounding medium ; they have no specific effect. The bodies 

 of bacteria killed by chloroform vapour are very toxic — more 

 so than filtered cultures — and there is evidence of the release of 

 poisons from the organisms when these undergo bacteriolysis in 

 the animal body. Allan Macfadyen, by grinding up typhoid 

 bacilli frozen solid by liquid air, produced a fluid whose toxic 

 effect he attributed to the presence of the intracellular poisons. 



The Immunisation of Animals against the Typhoid 

 Bacillus. — Earlier observers had been successful in accustoming 

 mice to the typhoid bacillus by the successive injections of 

 small and gradually increasing doses of living cultures of the 

 bacillus. Later, Brieger, Kitasato, and Wassermann found that 

 the bacillus when modified by being grown in a bouillon made 

 from an extract of the thymus gland no longer killed mice 

 and guinea-pigs. These animals after injection were moreover 

 immune, and it was also found that the serum of a guinea- 

 pig thus immunised could, if transferred to another guinea-pig, 

 protect the latter from the subsequent injection of a dose of 

 typhoid bacilli to which it would naturally succumb. Chante- 

 messe and Widal, Sanarelli, and also Pfeiffer, immunised 

 guinea-pigs against the subsequent intraperitoneal injection 

 of virulent living typhoid bacilli, by repeated and gradually 

 increasing intraperitoneal or subcutaneous doses of dead typhoid 

 cultures in bouillon. Experiments performed with serum derived 

 from typhoid patients and convalescents indicate that similar 

 effects occur in those who have successfully resisted the natural 

 disease. The serum of such patients has antibacterial powers, ■ 

 but there is no evidence that it contains any antitoxic bodies 



