THE BEGINNINGS OF LIFE. 353 



were first discovered about thirty years ago by J. Miiller, 

 pervading the spleen, kidney, and almost all the organs 

 and tissues (with the exception of the great nerve- 

 centres and the muscles of the trunk) of certain fresh- 

 water fishes. They often follow the line of the blood- 

 vessels, and are occasionally concentrated in such 

 enormous numbers as to form small whitish or yellowish 

 masses visible to the naked eye although individually 

 the organisms are only a very little larger than the 

 blood-corpuscles of the fish. Subsequent investigations 

 have revealed the fact that these rudimentary organisms 

 are to be met with habitually in the tissues of higher 

 as well as of lower organisms, where, for the most part, 

 they seem to exist without the slightest detriment to 

 the creatures which contain them. Six years ago, when 

 the cattle-plague raged with great virulence in this 

 country, some observers thought for a time that they 

 had detected its cause, when they found myriads of 

 these minute corpuscles imbedded in the flesh of ani- 

 mals which had succumbed to the disease. But a 

 distinguished helminthologist, Dr. Cobbold 1 , soon made 

 known the fact that such organisms might be met with 

 most abundantly in the healthiest mutton and beef; 

 and that they were always to be found in astonishing 

 numbers in the substance of the heart of sheep, oxen, 

 and other animals. They had, in fact, nothing what- 

 ever to do with the cause of the cattle-plague. Similar 

 parasites have been found, on several occasions, in 



1 'Lancet,' 1866, vol. i. p. 88. 

 VOL. II. A a 



