158 PRODUCTS OF DISEASE. 



many hundreds of years, and even more, and then 

 to germinate under favourable circumstances, and 

 so also may these granular germs of entozoa. After 

 the death of their parent they may mingle with the 

 atmosphere, or with the earth of the fields ; they 

 may be absorbed by plants, and contained in their 

 sap vessels, and during a thousand changes of situ- 

 ation remain torpid ; but suppose them to be taken 

 into the system of an animal an animal weakly or 

 inclined to disease, (for in such animals only do 

 they become developed,) and what is the result ? 

 The absorbed egg, taken perhaps into the system 

 with the food, is carried through the blood ves- 

 sels, threading their tortuous mazes, their minutest 

 capillaries, till at length it reaches a situation in 

 which its development shall begin. Its development 

 commencing, it remains stationary, it increases yet 

 more and more, reproduces in its turn myriads of 

 granules, and perishes. Thus, then, may the presence 

 of hydatids be accounted for. Animal bodies, be it 

 remembered, are not solid ; they are not like iron, 

 they are bundles of tubes ; they are porous, the air 

 permeates them, and they are ever changing their 

 constituents. 



It may here be objected, that if this be admitted, 

 hydatids ought to be at least very common in 

 healthy bodies. Not so ; the vigorous circulation 

 of the fluids in health, the rapid change of the con- 

 stituent particles of the body, the oxygenation of 

 the blood, may tend to prevent their development, 



