146 AIDS TO BACTERIOLOGY 



temperature being 37 C. On the surface of blood- 

 smeared agar it forms small transparent colonies, which 

 are perceptible with difficulty. Growth on ordinary agar 

 medium is slight and uncertain, but it grows better in 

 broth containing grape-sugar and glycerin. The organism 

 must be subcultured every eight days on blood- agar, or 

 its vitality will be lost. 



Pathogenesis. 'The period of incubation is twelve to 

 twenty-four hours. The disease may occur in an un- 

 complicated form, or may be accompanied or followed by 

 respiratory or gastro-intestinal lesions or neuroses, but no 

 case involving both respiratory and gastro-intestinal lesions 

 has been recorded. The simple form lasts from three to 

 five days, and the complicated from eight to ten, except 

 those affecting the nervous system, when the patient is 

 often months, or even years, in shaking off the effects, 

 and there are a few cases where insanity or paralysis has 

 resulted. It is not uncommon for the same patient to 

 have two attacks in one year, and in each fresh epidemic 

 those who have had the disease once are far more liable 

 to be attacked than those who have previously escaped. 



The bacillus varies greatly in virulence and in the type 

 of infection produced. The pneumococcus may be the 

 causative agent in many cases of so-called influenza 

 (Allen). In a small percentage symbiosis of the influenza 

 bacillus with the pneumococcus or Staphylococcus albus 

 occurs. Broncho-pneumonia of an epidemic type has 

 been caused by the influenza bacillus. Influenza is 

 transmissible to cats, and is the cause of ' pink eye ' in 

 horses. 



The Bacillus of Ducrey. 



The bacillus of soft sore ( Ducrey 's bacillus) is found 

 in the ulcers and buboes of soft chancre. It is minute 

 and generally arranged in groups or chains, mostly outside 

 the leucocytes. It does not stain by Gram, and is culti- 

 vated on blood -agar, producing small shining grey 

 colonies, or in guinea-pig's blood. It produces the disease 

 on inoculation of the human subject. 



The Koch- Weeks Bacillus. 



This small bacillus is the cause of an acute contagious 

 conjunctivitis Morphologically it resembles the influenza 



