544 DR DAVY ON THE URINARY SECRETION OF FISHES. 



weighing about a pound and a half, taken in the same lake, and in the same 

 month as the trout, — there was a little mucus-like matter suspended in its fluid 

 contents. The fluid was rendered turbid by admixture with alcohol. It cleared 

 on rest, from the subsidence of the precipitated matter. The clear solution, de- 

 canted and evaporated gently, yielded crystals approaching in form those afforded 

 by a weak solution of muriate of ammonia similarly treated. Redissolved on the 

 addition of a minute portion of nitric acid, and again evaporated, crystalline 

 plates were obtained very like those of the nitrate of urea. Subjected to the 

 temperature required for detecting the presence of lithic acid, the result was ne- 

 gative, — the hue produced was yellow, without the slightest tinge of purple ; — 

 and the mucus-like matter similarly tested afforded a like result. 



The urinary bladder of the pike {Esox lucius) is very small. I have always 

 found it empty. In the ureter* of one of about two pounds, taken in Winder- 

 mere in May, a few delicate yellowish flakes were detected. These, under the 

 microscope, exhibited no characteristic appearance; acted on by dilute nitric 

 acid, however, they were in great part dissolved ; and when evaporated with a 

 graduated heat to dryness on a support of thin glass, the purple stain distinc- 

 tive of lithic acid was produced, and it was so strong, that it coloured a propor- 

 tionally large quantity of water. 



The ling [Lota molva) has a comparatively large urinary bladder. From the 

 bladder of one,— a fish of about four feet long, taken in the Mount's Bay, in Corn- 

 wall, in the month of June, — a small quantity, about a drachm, of nearly colour- 

 less fluid was obtained, in which a few flakes resembling lymph were sus- 

 pended. These flakes were tested for lithic acid, but with a negative result. 

 The fluid was coagulated by heat, by nitric acid, and by alcohol, indicating the 

 presence of a notable proportion of albumen. The alcoholic solution, after the 

 separation of the precipitated albumen, evaporated to dryness at a low tempera- 

 ture, yielded, after the addition of a minute portion of nitric acid, crystals which, 

 seen under the microscope — they were too small to be seen without this aid — 

 resembled so closely those of nitrate of urea, that I had little hesitation in coming 

 to the conclusion that they were this compound. 



The common ray (Raia balis) is provided with two small bladders, each dis- 

 tinct, and neither of them communicating directly with the kidneys. In a male, 

 examined in November, they were found distended with a nearly colourless lim- 

 pid fluid, in which, placed under the microscope, were seen many small globules, 

 and a few spermatozoa. This fluid, evaporated at a low temperature, yielded a 

 colourless residue, in which were minute crj^stals of common salt ; and, acted on 



* Professor Owen, in his Lectures on the Comparative Anatomy of the Vertebrate Animals 

 (Part i., p. 223), describes the bladder of the pike as communicating with the kidneys by a single 

 common ureter ; in most instances I have found the communication such, but in one fish, one of 

 six pounds, it was by two. 



