Prof. Ehrenherg's Researches on tlie Infusw'ia. 211 



In conformity with the great axiom of scientific observation, 

 to measure every thing which is capable of measurement, Dr 

 Ehrenberg has not neglected to express in numbers the dimen- 

 sions not only of the totality, but also of the integrant parts of 

 these beings, placed as it were at the verge of organized nature. 

 For this purpose he uses a glass micrometer, constructed by 

 Dollond, which gives directly the ten-thousandth part of an 

 inch, and permits of a much smaller quantity being correctly 

 estimated, as it contains the astonishing number of 400 equal 

 parts distinctly cut in glass within the space of half a line. By 

 means of a micrometer screw, which has been since constructed 

 by Pistor of Berlin, he has been enabled to measure directly 

 15505 of an inch, or jo^fjo of a hne, a degree of minuteness 

 which is never necessary in actual practice. 



1. Digestive System. — By the use of colouring matter in the 

 way above mentioned, a digestive system has been demonstrated 

 in all the genera of this class of animals, distinctly characterized 

 by Miiller. This fact Dr Ehrenberg states in the following 

 proposition : " All true infusoria, even the smallest monads, 

 are not a homogeneous jelly, but organized animal bodies, dis- 

 tinctly provided with at least a mouth and internal nutritive 

 apparatus." In none has the cuticular absorption of nutritive 

 matter ever been observed, which had been the opinion of all 

 previous writers upon the subject, not froin any positive obser- 

 vations, but merely from their inability otherwise to explain the 

 nutrition of these animals. Generations of these transparent 

 gelatinous bodies may remain immersed for weeks in an indigo 

 solution, without presenting any coloured points in their tissue, 

 except the circumscribed cavities above referred to ; and when 

 in a state of activity, the minute particles of indigo and carmine 

 are seen to hurry rapidly over the whole surface of their trans- 

 parent bodies, in order to reach the mouth, generally situate at 

 one or other of their extremities. Indeed there is no necessity 

 of having recourse to such a supposition, when we can clearly 

 see the prehension of colouring particles, their reception into a 

 mouth, and conveyance from thence into an internal stomach or 

 stomachs. 



The alimentary canal presents, as in the other classes of the 



