482 SPOEADIC DISEASES. 



infecting ; while the same plants or waters, containing identical 

 chemical elements, are at other times or places innocuous. It 

 will further explain why only a certain proportion of the animals 

 or men exposed to the morbid influence succumb to it ; while 

 the remainder, whose systems or vital fluids are in a condition 

 chemically incompatible with the propagation of the bacteria, 

 escape. It is quite in keeping with the fact that the disease is 

 produced in widely different conditions of climate, vegetation, 

 soil, geological formation, and management ; and that no com- 

 bination of these is able to produce it, unless the disease germ 

 has been introduced. It explains, too, the permanent preserva- 

 tion of the virus in cheese and other comparatively stable 

 products of the sick. It is equally in keeping with the following 

 circumstances, relating to what may be considered predisposing 

 causes of the disease : — 



" The excess of effete matters in the blood evidently favours 

 its development. Thus, overwork, severe exertion — even for a 

 limited time — want of sleep (as in the case of the members of a 

 family watching with a sick relation), a fit of constipation, or a 

 slight attack of malarial fever, all strongly conduce to the 

 development of the malady. It is curious to note that children 

 often suffer less than adults, probably because their emunctories 

 are usually more free, and they are less exposed to exhausting 

 and depressing conditions. In infected cattle, the symptoms 

 are easily developed or aggravated by subjecting them to fatigue; 

 and in milk-sick districts, it is a common practice to test the 

 soundness of stock by giving a good run before purchasing. 



" Another very remarkable fact is, that milch cows rarely show 

 the disease, though conveying it to other animals through their 

 milk. Dr. Phillips says — ' It is not unusual, where persons 

 suffer from this disease, to find, at the same time, calves using 

 the same cow's milk sick with 'tremUes;' while the cows are to 

 all appearance in perfect health. The dry cattle are much more 

 frequently attacked with 'trembles' than cows wliich are secreting 

 milk in abundance.' To the same purpose Dr. Schmidt remarks 

 — ' Cows giving milk do not show the disease at all, but their 

 calves have it all the time as long as they suck the milk ; dogs 

 fed on milk get it.' Dr. Phillips says — ' A calf gets it from tlie 

 cow in the milk, — the calf dies ; and the pigs which eat the 

 carcase get the disease and die ; the dog which eats the pig, and 



