453 



have been fifteen ; of those with a urinary bladder he found a fluid 

 only in three, the Perch, Ling, and Ray ; and in those without 

 this organ, only in two, in their ureters — those of the Pike and 

 Turbot. 



His experiments to ascertain the composition of the secretion were 

 attended mostly with negative results. In one instance, that of the 

 Pike, he detected lithic acid ; in some others there were indications 

 of the presence of urea in the fluid urine. 



The conclusions he ventures to draAV are, that the secretion is 

 small in quantity, mostly liquid, and that urea or some other analo- 

 gous nitrogenous compound is its principal ingredient. 



For the sake of comparison and further inferences, he notices the 

 secretion in other classes of animals, laying emphasis on the propo- 

 sition, that the quality of the secretion in each is more regulated 

 by the structure of the urinary organs than by any other circum- 

 stance, and that the quality of the food, whether animal or vege- 

 table, neither exercises an influence on the quantity of the nitroge- 

 nous excretion nor on its kind. He points out how, irrespective of 

 the nature of the food, urea is the chief ingredient of the urine of 

 the Mammalia, and of other animals provided with a urinary blad- 

 der ; how the alkaline lithates and uric acid take the place of urea 

 in those destitute of this organ, such as birds, serpents, lizards, in- 

 sects, mollusca, and some lower in the scale of organization, as the 

 myriopoda ; and further, how in the instance of scorpions and 

 spiders another compound is substituted for the soluble urea, viz., 

 guanine, which, like the lithates, is excreted in the state of a soft 

 solid. 



He concludes with adverting to the harmonious relation of func- 

 tions in the animal economy, and the close alliance in action between 

 the lungs and the kidneys ; adding, that as their activity seems 

 generally to be in accordance, and as in fishes the temperature is 

 low, and little carbonic acid evolved, it may be presumed, as his ex- 

 periments seem to show, that their urinary secretion is proportion- 

 ally inconsiderable. And hence, as their digestive powers are great, 

 it may further be inferred that most of their food is assimilated, and 

 is used in administering to their growth. This view he thinks is in 

 agreement with, and helps to explain some of their peculiarities, 

 such as we witness in the salmon, the history of which, of late years, 

 haa been so carefully and successfully studied. 



