388 ON THE ORIGIN OF ENTOZOA 



that the propagation of TcemcB admits of a ready explanation, 

 when we remember how fish are transported into lakes and 

 ponds, recently stagnant, by aquatic birds, or how the Voriicella 

 rotatoria is generated in rain-water contained in the pipes 

 under the roofs of houses, and other lofty situations. He 

 thinks that this mode of propagation is indubitable as regards 

 the TcsnicB at least, the eggs of which he supposes to be every 

 where distributed (external to the body), and that by accident 

 they become transported into other animals through the medium 

 of nutriment. The following is a summary of his arguments : — 



1. Worms are by far the most common in large cities, or in 

 other situations much frequented either by men or animals, 

 particularly under the influence of bad food and insufficient 

 ventilation ; where humidity of the atmosphere and soil may 

 preserve the ova and protect them whilst out of their natural 

 situation ; where the water of cisterns, closed wells, or rivers 

 receiving the filth and refuse from the city itself, is used as 

 the common drink : so, on the other hand, all the species of 

 worms are infinitely more uncommon in the deserted and only 

 recently- inhabited regions of Russia and Siberia, or among the 

 shepherds and Nomades, or among wild animals, than in the 

 more civilized and thickly-populated parts of Europe. 



2. The place of abode of certain species of worms is always 

 the same, whether it be in warm-blooded animals, birds, or 

 fishes ; and doubtless it is in these animals alone that they 

 would meet with that degree of temperature and kind of nutri- 

 ment necessary to their development, and in the absence of 

 which they would perish. 



3. Worms have been observed in new-born animals, and 

 even in the foetus i?i utero. 



And lastly, it has not been an uncommon observation, that 

 the Tcenice has materially aggravated an epidemic; however 

 this may be, it is certain that the FercB, or beasts of prey, are 

 notoriously infested with worms ; that the GUres, who carefully 

 masticate their nutriment, are less commonly so ; and that it 

 is a very rare occurrence comparatively to discover them in the 

 Ruminantia, in whom the food undergoes extreme commi- 

 nution. Carnivorous birds and those which are domesticated 

 are very subject to them; and among the migratory fish and 

 those which are tenacious of life, parasitical animals abound. 



These, then, are the arguments which this celebrated man 



