DIGESTION OF ANIMALCULES. 129 



that many of our metallic or earthy colouring 

 materials immediately poison these creatures, when, 

 of course, the experiment fails. Ehrenberg tried 

 in vain with the indigo and gum-lac of commerce, 

 these substances being always contaminated with a 

 slight admixture of white lead, which acts as an in- 

 stantaneous poison ; but with pure indigo, or pure 

 carmine, the experiments were successful. 



When a minute portion of a very weak solution 

 of indigo is added to a drop of water containing 

 vorticella, an animated scene ensues. Eager for the 

 food, which they swallow with avidity, they throw 

 the cilia into rapid action, producing currents in the 

 water, hurrying with them the particles of the 

 indigo in gyrations converging to the mouth. In a 

 short time, a number of dark blue circular dots 

 begin to show themselves on the transparent body 

 of the animalcule, which are occasioned by the 

 particles of the indigo accumulated ;in these situ- 

 ations ; they also make manifest the intestinal tube, 

 and their progress can be gradually traced through 

 its extent. It is thus by a series of experiments 

 that Ehrenberg was at length enabled to determine 

 the number of the sacs, or stomachs, and the course 

 of the intestinal tube. But it appears that all the 

 sacs are not filled at the same time ; many con- 

 tinue long without receiving any particles of colour- 

 ing matter, and the whole range of the alimentary 

 tube is not simultaneously tinted. The num- 

 ber of sacs thus distinguished, amounts to two 



