CHAPTER VIII. 



Cholera. 



Cholera a Parasitic Disease — Early Observations on the Comma Bacillus 

 — Characters — Methods of Staining — Methods of Isolation — Use of 

 Plate Method in Practical Public Health Work— Tube Cultures— 

 Motility of cholera bacilli — Potato, Blood-serum, and Milk Growths 

 — Behaviour in Water and Sewage — Infection of Man through Agency 

 of Bacillus — Early Inoculation Experiments — Koch — Nicati and 

 Rietsch — Macleod — Difficulties — Cholera in Guinea-pigs — Position of 

 Bacilli in Tissues — Presence of spores doubtful. 



On account of its general interest there are few examples 

 that can more appropriately be taken to illustrate the rela- 

 tions between a special bacillus and a special disease than 

 that afforded by Koch's discovery of the comma bacillus 

 in cases of Asiatic cholera, and its relations to that disease. 

 The study of the disease itself, since its appearance in this 

 country in the great epidemic of 1832, has had a peculiar 

 fascination for epidemiologists and skilled hygienists. Its 

 development, behaviour, and whole general history appeared 

 to be shrouded in mystery, and phenomena, the explana- 

 tion of which seemed to be utterly beyond the powers of 

 experts of all kinds to give, were at one period constantly 

 being observed, recorded, and discussed. Now, however, 

 through the laborious but brilliant researches initiated by 

 Pettenkofer at the head of one school, and by Koch in a 

 very different one, much of this air of mystery has been dis- 

 pelled, and many of the doubts and difficulties that sur- 

 rounded the subject have been gradually cleared away as 

 workers under one or the other of these great leaders have 

 gained fresh knowledge and elucidated new facts. Take, 

 for example, the question of the spread of cholera from 

 its home in Lower Bengal, in the delta of the Ganges, 

 to surrounding districts and distant countries. At first such 

 spread was thought to be most erratic and inexplicable. 

 Now, however, although it appears from time to time to have 



