PARASITES OF ANIMALS. 331 



The septic element disengaged from these putrid fragments 

 retarded the development of the strongyli, but failed to arrest 

 it. And even if the experimental troughs contained a very 

 large amount of water, the strongyli disengaged themselves 

 in great numbers from the morsels of putrid lungs ; and, 

 though reduced to a putrid pulp, the eggs could be seen 

 amidst this ready to open, and the young worms escaping 

 from their envelopes." 



" It is in fresh water that the worms are most readily devel- 

 oped, and live longest after leaving their natural habitat. 

 Water is a transition medium in which the worm which has 

 abandoned one animal can survive, waiting a favorable oppor- 

 tunity to enter another. In this medium the strongyli are 

 hatched and live for entire weeks and months without percep- 

 tible growth, that is to say, they preserve their primary mi- 

 croscopic proportions. They can there resist sudden changes 

 of temperature and the deleterious influence of putrid matters, 

 whilst they wait an occasion of entering with the aliments into 

 the body of a new host, in whose air passages they find the 

 conditions necessary to their assuming the attributes of sexu- 

 ality and reproducing their kind. 



Causes. — These are, of course, primarily and mainly the 

 introduction of the embryo strongyli into the system, but 

 many other conditions may combine as accessory to the pres- 

 ervation and propagation of the worms. Thus, wet seasons, 

 by providing moisture or pools for the preservation of the em- 

 bryos, contribute to their wider diffusion. In keeping with 

 this we find the first record of the disease as existing in the 

 low wet grounds of Holland, and the two by Despallens as 

 occurring in the wet summers of 1795 and 1811. The same 

 holds good in England alike as regards the prevalence of the 

 disease in the low fenny counties, and in rainy seasons ; and 

 these remarks apply to other animals as Avell as calves and 

 lambs. A donkey, from the low meadows at Hammersmith, 

 London, rarely failed to yield a supply of the strongyli. And 

 in the present year, which has proved unusually cold and wet 

 in the British Isles, we are not surprised at the serious com- 

 plaints of the extraordinary death of pheasants from gapes. 



