130 Dr. J. M. Hobson on 



whicli accumulates through a certain degree of stagnation caused 

 by the impediment of the tides. The delta of the Ganges is 

 looked upon as the home of cholera, and there it is to be found 

 all the year round. Since the introduction of a good water 

 supply to Calcutta, cholera has been reduced there 60 per cent. 

 In another great delta, that of the Yang Tze at Shanghai, cholera 

 is also endemic, but it is not present all the year round as at 

 Calcutta. It comes regularly after two months of hot summer. 

 This points to the soil temperature as an important factor. It 

 is true that the temperature of the soil at some depth does not 

 reach its maximum till after the atmospheric maximum is 

 reached. The cholera spirillum is not difficult to cultivate. 

 When grown in peptonised gelatine, especialhj when free oxygen is 

 excluded, it generates a very deadly alkaloid, which will produce 

 in animals some of the characteristic symptoms of cholera. 

 When the spirillum can get a footing in tlie mtestines, and the 

 soil is not unfriendly, it takes up its abode there, getting into 

 the secretory crypts, and even beneath the epithelium of the 

 mucous membrane, but not, it appears, into the blood-stream or 

 internal organs. Yet to get to the intestines it must pass the 

 barrier of the stomach, and as it cannot stand acids, it would 

 appear to have a poor chance of getting to the intestines, whose 

 contents are alkaline. Yet that it does only too often reach the 

 intestines alive indicates that it does so either while gastric 

 digestion is in abeyance or the stomach in an unhealthy state. 

 Certain it is that persons who have got the cholera have often 

 been previously suffering with dyspeptic symptoms. Although 

 cholera does not appear to be catching from one to another in 

 the ordinary way, as small-pox and scarlet fever are, it is never- 

 theless indirectly catching. The people who wait upon the 

 patient, or who bury him when dead, do not often catch the 

 disease, while the person who washes the soiled garments later 

 on may do so. The explanation offered is this : during the day 

 or so which elapses before the articles are washed they have been 

 living a non-parasitic life, and have become hardier than the 

 pampered race which have been living a parasitic life, and have 

 thus become hardier and better able to force their way into a new 

 host. 



Tuberculosis. — The tubercle bacillus was discovered in 1883 

 by Koch. It is a slender rod from xt^oo ^^ boVo i'^^'^ ^^ng and 

 about T-fiioo 'wide. It has not been found as yet free in nature, 

 that is to say, so far as we know it is a pure parasite ; but after 

 a great deal of trouble a way has been found to cultivate it 

 artificially. It is not motile, and is very slow growing. When 

 it finds its footing in a living body it does not travel with the 

 blood-current like anthrax, nor swarm in the intestine like 

 cholera, but takes up its abode in the solid tissues, there setting 



