54 THE MECHANICAL FUNCTIONS. 



and apparently lifeless state when the pond is eva- 

 porated, will, in like manner, revive, in a very 

 short time, on being again immersed in water. The 

 same phenomenon is exhibited by the Filaria oculiy 

 a thread-like parasitic worm, infesting the cornea 

 of the eye of the horse.* 



Both the composition of the fluid and the texture 

 of the solid parts of animal and vegetable bodies 

 are infinitely varied, according to the purposes they 

 are designed to serve in the economy. Scarcely 

 any part is perfectly homogeneous ; that is, com- 

 posed throughout of a single uniform material. 

 Few of the fluids are entirely limpid, and none are 

 perfectly simple in their composition ; for they ge- 

 nerally contain more or less of a gelatinous matter, 

 which, when very abundant, imparts to them vis- 

 cidity, constituting an approach to the solid state. 

 Many fluids contain minute masses of matter, gene- 

 rally having a globular shape, which can be seen 

 only by means of the microscope, and which float 

 in the surrounding liquid, and often thicken it in a 

 very sensible manner.t We next perceive that 

 these globules have, in many instances, cohered, so 

 as to form solid masses ; or have united in lines so 

 as to constitute fibres. We find these fibres col- 

 lecting and adhering together in bundles ; or inter- 

 woven and agglutinated, composing various other 

 forms of texture; sometimes resembling a loose net- 

 work of filaments; sometimes constituting laminae 

 or plates; and, at other times, both plates and fila- 



* De Blainville, Annales des Sciences Natu relies ; x. 104. 



t Globules of this description are found not only in the blood, 

 and in milk, where they exist in great abundance, but also in the 

 lymph, the saliva, and even in the aqueous humour of the eye. 



