DIFFUSED CIRCULATION. 169 



ance, for it is founded, perhaps, more on our imperfect means 

 of investigation, than on any real differences in the pro- 

 cedures of nature relative to this function. When the juices, 

 either of plants, or of animals, are transparent, their motions 

 are imperceptible to the eye, and can be judged of only by 

 other kinds of evidence; but when they contain globules, 

 differing in their density from that of the fluid, and there- 

 fore capable of reflecting light, as is the case with the sap of 

 the Chara and Caulinia, we have ocular proof of the ex- 

 istence of currents, which, as long as the plant is living and 

 in health, pursue a constant course, revolving in a regular 

 and defined circuit; and all plants which have milky juices 

 exhibit this phenomenon. Although the extent of each of 

 these vegetable currents is very limited, compared with the 

 entire plant, it still presents an example of the tendency 

 which the nutrient fluids of organized structures have to 

 move in a circuit, even when not confined within vessels or 

 narrow channels; for this movement of rotation^ or cyclosis, 

 as it has been termed,* whatever may be its cause, appears 

 always to have a definite direction. The current returns 

 into itself, and continues without intermission, in a manner 

 much resembling the rotatory movements occasionally pro- 

 duced in fluids by electro-magnetism. t 



Movements, very similar in their appearance and cha- 

 racter to those of vegetable cyclosis, have been recently dis- 

 covered in a great number of polyferous Zoophytes, by Mr. 

 Lister, who has communicated his observations in a paper 

 which was lately read to the Royal Society, and of which 

 the following are the principal results. In a specimen of 

 the Tubular ia indivisa, when magnified one hundred 

 times, a current of particles was seen within the tubular 

 stem of the polype, strikingly resembling, in the steadiness 

 and continuity of its stream, the vegetable circulation in the 



* See pages 41 and 42 of this volume. 



f So great is this resemblance, that it has led several physiologists to as- 

 cribe these movements to the agency of electricity; but there does not, as 

 yet, appear to be any substantial foundation for this hypothesis, 

 VOL. II. 22 



