Nervous System of the Infusoria. 61 



contractions of the nervous fibres in the nerves ; but this charac- 

 ter is only sufficient for nerves of considerable bulk, and some- 

 times it may be mistaken for the fibres of tendons, as, for ex- 

 ample, for the tendons of the toes of frogs. Experiments with 

 the galvanic pile cannot go beyond a certain degree of minute- 

 ness. The only means which have been hitherto discovered, 

 whereby to arrive at certainty concerning the nature of a slender 

 filament which is suspected to be a nerve, is to trace its course 

 to the branch whence it proceeds, and thence to its junction 

 with the spinal cord, or the brain, or with a distinct ganglion, 

 cr, finally, to recognise it penetrating into one of the organs of 

 sense. Unfortunately, microscopic researches upon nervous mat- 

 ter are not far advanced ; and it almost appears that the tran- 

 sparency of the nervous matter in microscopic animals, is an in- 

 surmountable obstacle to our cognizance of the existence of this 

 substance, and of its structure. 



But in spite of these unfavourable circumstances, M. Ehren- 

 berg never became a convert to the opinion so generally adopted, 

 that the nervous matter is intimately mixed up with, and not 

 separated from, the body even of the most irritable of the Infu- 

 sores ; on the contrary, he conceives that certain organs in these 

 animals are the brain and nerves. This opinion is founded upon 

 three considerations, 1^^, The possibility of demonstrating the 

 existence of organs resembling in form the brain and nerves ; 

 2^/, Their arrangement within the body ; and, 3J/^, Their dis- 

 tinct communication with the eyes. 



As to the first of these considerations, the whole of his ob- 

 servations upon the special organs of thelnfusores, and their com- 

 parison with the organs of superior animals, have demonstrated 

 to him that the number of the organs, or the sum of organiza- 

 tion, was remarkably equal in these two kinds of animals. It 

 would certainly be ridiculous and inadmissible to speak of nerves 

 and of a nervous system in animals which had no other organs, 

 or which presented mere indistinct traces of them, as unhappily 

 has sometimes been done. But our author has discovered in 

 the Rotatory animals, \st, A system of organs of nutrition, with 

 all its details ; 2J, A double sexual system, observed in all its 

 development; 3J, A more extensive vascular system, the exist- 

 ence of which is at least highly probable ; and, 4M, Distinct 



