DIFFUSED CIRCULATION. 1G9 



nnce, for It is founded, perhaps, more on our Imperfect means 

 of investigation, tlian on any real diflercnces in the ])ro- 

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

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

 are imperccptihlc 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 tlie sap of 

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

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

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

 and deflned circuit; and all ])lants 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 examj)lc 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 rolalion, or cf/clo.siSj 

 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 Tubulai'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 docs not, as 

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



Vol. II. 22 



