CHOLERA. 107 



healthy crew may bring with them, in the closed hold of 

 their ship, the germs of disease, which, after their dismis- 

 sal, may pestilentially affect the " stevedores" who dis- 

 charge her, or only the laborers ivho disturb her ballast. 



We can thus, too, explain the usual pause between the 

 first set of cases caught by visitors to, or laborers on 

 board, the ship, and the attack upon the inhabitants of 

 the vicinity. This curious interval, noticed by almost 

 every writer, occupies about ten to fifteen days, whilst 

 the period of incubation, after exposure to a known source 

 of infection, is only about five days. (Vach.) 



This interval is only to be explained by the supposition 

 that germs, of some kind, have gained a footing on shore, 

 and have germinated and grown more numerous. It is the 

 crop in the hold which produces the first set of cases* It 

 is the crop on the land which causes the second. 



It is only through the action of some organic cause, that 

 we can explain the tenacity of the attachment of yellow 

 fever to certain ships, and these, too, among the cleanest 

 and best aired vessels in the British service. The Sybille 

 had three several epidemic attacks between the 23d of 

 June, 1829, and the middla of April, 1830. Two of these 

 occurred while at sea. In the West India service, cer- 

 tain ships have usually an outbreak on going into even a 

 healthy harbor. 



Perhaps no disease has so much puzzled the etiologist 

 as cholera. Its singular local origin, its yet more singular 

 progress, its apparent inconsistencies, its diffusion from a 

 tropical point over the habitable globe, and especially its 

 invasion, in winter, of the frozen steppes of Tartary and 

 Russia, all tend to confuse the observer of epidemics. At 

 one time, slowly, against the monsoon, it advances on a 

 long geographical line, at the rate of from one to two 



