THE INFECTIOUS DISEASES. 227 



what larger than the influenza bacillus, and tend to form threads. This organism has 

 been called the pseudo-influenza bacillus B. pseudo-influenza. Its pathogenic capaci- 

 ties are not clear, but it evidently differs in this respect from the genuine influenza ba- 

 cillus. In stained specimens of exudate the pseudo-bacillus may be mistaken for its 

 relative. 



Another bacillus of this group, B. conjunctivitidis, has been found in conjunctival 

 catarrh by several observers in various countries. 



TYPHOID FEVER. 



Typhoid fever is an acute infectious disease incited by the Bacillus 

 typhosus. The reaction of the body to this bacillus is usually mani- 

 fested by characteristic lesions, especially by hyperplasia and necrosis 

 in the lymphatic structures of the intestines and the mesenteric lymph 

 nodes, and in the spleen, as well as by the more general alterations inci- 

 dent to toxaemia and septicaemia ; but the infection is occasionally of the 

 septieaemic type without characteristic local lesions either in the intes- 

 tines, or meseuteric nodes, or other viscera. 



THE BACILLUS OF TYPHOID FEVEE. 



The presence of a bacillus, called Bacillus typhosus, in various parts 

 of the body in typhoid fever, in a considerable proportion of the cases 

 examined, has been well established by a large number of observers. 

 This bacillus does not occur in the body, so far as is known, except in 

 connection with this disease. 



Characters of the Bacillus Typhosus. 



The typhoid bacillus is usually about three times as long as broad, being about one- 

 third as long as the diameter of .a red blood cell. It is rounded at the ends, motile, 

 aerobic, facultative anaerobic, and asporogenous. It grows readily at room tempera- 



ture on the ordinary media. In cultures the bacilli often 



cling together end to end, forming threads (Fig. 108). 



During artificial culture in nutrient broth a poisonous 

 albuminoid product or products are formed which have 

 been named typhotoxin. Injection of this into the rabbit 

 may in addition to general toxic symptoms induce hyper- 

 plasia of the intestinal lymph nodes. 



Inoculations of the typhoid bacillus into animals, 

 F,G. i08.-BACiu.rs TYPHOSUS. , wh . le not ^^fog a ft m& s e fa all respects like that in 



the human subject, may cause death with symptoms and lesions as closely resembling 

 those in man as we are often able to produce in animal experimentation. Although 

 similar effects may be induced in animals by inoculation with other germs, the evi- 

 dence that typhoid fever in man is produced by the typhoid bacillus, and by this alone, 

 is altogether so strong as practically to amount to a demonstration. 



It is probable that the more characteristic symptoms and lesions of 

 typhoid fever are largely due to the absorption of toxic substances which 

 are produced as the result of the life processes of the bacteria at the 

 point of their greatest accumulation and activity. It should, however, 

 be borne in mind that the typhoid bacillus, as is the case with many 



