118 Zoological Collections. Invertebrata. 



tions and dilatations of the coagulum, sometimes veiy much resembling the 

 contractions of a muscle. As these motions appear to take place indepen- 

 dently of any extrinsic agency, they were supposed to depend on some faculty 

 of spontaneous motion in the globules, which was believed to contribute 

 materially to advance the blood through the capillary vessels. 



Dr Czermack has observed a peculiar motion of the blood-globules exterior 

 to the vessels in some of the lower tribes of animals, such as Mollusca, 

 Crustacea, &c. but in none so distinctly as in the proteus, and larva of the 

 salamander ; in which last animal, he shewed the phenomenon to Professor 

 Lichtenstein. One of the vessels of the gills of the larva of Salamandra 

 atra was cut through, and the blood received on the object-glass of the 

 microscope; the globules were then seen to move round, sometimes in 

 circles, at other times in ellipses ; at a few points, an irregular motion 

 forward and backward was observed. This phenomenon lasted some 

 minutes, and, in the opinion of those who witnessed it, could be ascribed 

 neither to physical attraction and repulsion, nor to the presence of infusory 

 animalcules. It was visible only in full-blooded and lively specimens, in 

 which the gills had attained a certain degree of perfection. Dr Czermack 

 ascribes the non-appearance of this supposed spontaneous motion within 

 the blood-vessels to the influence of the nervous system. 



In reference, generally, to these observations on the blood, I must confess 

 I have never been able to perceive a motion in that fluid, which could, on any 

 ground, be considered as spontaneous ; and with, regard to the phenomena 

 observed by Dr Czermack, I am much disposed to think that they must be 

 referred to a very different cause from what he assigns, viz. to a peculiar 

 property in the skin of the animals in which he made his observations, of the 

 existence of which property Dr C. seems not to have been aware. In a paper 

 published in the Edinburgh Medical Journal, for July 1830, and extracted 

 into your Journal, (Vol. II. p. 334,) I have shewn, that, in the larva of the frog 

 and salamander, the mollusca, and other inferior tribes of aquatic animals, the 

 external covering of the body generally, but especially of the respiratory 

 organs, possesses the power of impelling the water contiguous to it in a 

 determinate direction along the surface, by which means a constant current 

 is kept up, and the blood exposed to the influence of successive portions of 

 the surrounding element ; this peculiar provision effecting, in those creatures, 

 the same purpose as the respiratory muscles in more perfect animals. The 

 property, to which the production of currents is owing, remains a considerable 

 time in parts which have been detached from the rest of the body, especially 

 in portions of the gills. Now, Dr Czermack observed the phenomena, 

 described by him, chiefly in animals in which the property alluded to exists ; 

 and from the manner in which the observation is stated to have been made 

 on the larva of the Salamandra atra, as well as from some more or less 

 direct expressions used by the narrator, it seems to me very probable, that 

 the supposed spontaneous motion of the blood-globules had been observed 

 in the vicinity of the gills, and had been occasioned by the before mentioned 

 influence, exerted by these organs on the surrounding fluid, and on small 

 bodies floating in it. If, in fact, a portion of the external gills be cut off" 

 from the larva of the frog or salamander, and brought under the microscope, 

 the globules of blood which have escaped at the cut part will be seen to be 

 moved about in a manner not unlike that described by Dr C. ; for though 

 the respiratory currents run in one direction from the root of the gill to the 

 points of the branches, yet, as they change their direction at the points, and 

 turn off" to a side, many of the globules are carried back, so as to come again 

 within reach of the current, and are thus continually hurried round with a 

 circular or elliptical motion. But if I be right in inferring, that the motion 

 observed by Dr Czermack was of this sort, it is obviously incorrect to 

 ascribe it, as he has done, to a powet of spontaneous motion in the globules, 

 which are entirely passive, and whose motion differs in no material respect 



