QN THE BRITISH ANNELIDA. l73 



vity. This is an inferential datum, which proves that the peritoneal fluid, 

 although consisting of a large proportion of sea-water, is nottvithstanding 

 an organic Jiuid. This fluid, in the instances of the TerebellcB and Arenicola, 

 in which it is abundant, is rendered opake by the addition of nitric acid, 

 proving the presence of albumen ; and by standing, a coagulum is formed, 

 sufficient to prove the presence of fibrine ; and the microscope establishes the 

 existence of highly organized compound corpuscles. 



Now, that the basis of this fluid consists of sea-water, is rendered almost 

 certain by the following simple expedient : — If the peritoneal fluid of 

 Arenicola or Terebella nebulosa be collected in adequate quantity and care- 

 fully filtered, and the clear liquor be then submitted to evaporation, the 

 crystalline products will be found identical with those resulting from the 

 evaporation of simple sea- water. The inference then is probable, that the 

 fluid bases of the peritoneal fluid in all Annelida must consist chiefly of 

 sea-water ; nor does inductive caution here forbid the generalization sug- 

 gested by the preceding facts, that in the lower forms of life the surrounding 

 medium is assimilated with remarkable rapidity ; that sea-water under such 

 circumstances readily assumes the character of an organic fluid \ in other and 

 more specific language, that sea-water is vitalized with wonderful facility 

 by the solid organic elements contained in the peritoneal fluid. It is per- 

 fectly impossible to demonstrate any direct communication between the peri- 

 toneal cavity and the exterior. The channel of communication lies through 

 the alimentary canal ; the water is swallowed, and under the agency of the 

 intestinal, glandular and vascular systems, it receives the first impulse to or- 

 ganization ; thence it probably passes by direct transudation into the general 

 peritoneal chamber. The anterior extremity of the intestinal canal is endowed 

 with the power of readily absorbing this fluid, while the caudal end no less 

 readily gives it exit into the rectal division of the same canal ; and this is the 

 mechanism by which the peritoneal cavity is supplied with its fluid contents. 

 Whether the peritoneal fluid is organically capable of maintaining the 

 nutrition of the solid structures of the system, cannot be directly proved; 

 but it is scarcely susceptible of doubt, from the intricate manner in which 

 the true blood-vessels coil in the midst of the fluid contents of the general 

 cavity, that the former must absorb from the latter the elements from which 

 the true blood is afterwards manufactured ; that in fact it presents the same 

 relation to the contents of the proper blood-system of vessels, as the chyle of 

 the higher animals does to the true blood ; the peritoneal fluid of the An- 

 nelid differing from the chyle of the mammal only in the fact that the latter 

 is contained in vessels, while the former rolls in a capacious chamber. 



The absorbent power of the peritoneal fluid for oxygen is increased 

 in proportion as its density is increased ; this property the author deduces 

 from his experiments on salt water. When this fluid is evaporated to dif- 

 ferent degrees of density, and allowed to stand for a day or two, the gases 

 extricated by boiling bear a direct proportion in volume to the specific gra- 

 vity. Liebig has recently shown that the absorbent property of water for 

 carbonic acid is very much increased by the addition of phosphate of soda, 

 or a solution of sulphate of copper saturated with nitric oxide. These and 

 analogous facts render the inference highly probable, that the peritoneal 

 fluid, in virtue of its augmented absorbent power, readily withdraws oxygen 

 from the circumfluent medium, and brings this vitalizing gas in a more con- 

 densed and concentrated form into immediate contact with the true blood 

 and the solid structures of the body. This mechanism therefore, so far from 

 diminishing, actually multiplies the aerating influence of the surrounding 

 medium. The respiratory process ia rendered not less, but more efficient, by 



