332 THE SECRETIONS: 



urine being alkaline, are, for the most part precipitated, but 

 likewise form a delicate film on the surface. When this is the 

 case, the pellicle is very thin and readily sinks to the bottom. 

 Under the microscope crystals of ammoniaco-magnesian phos- 

 phate, and an amorphous matter very similar to kystein, but 

 consisting of phosphate of lime, are observed : this likewise 

 differs from kystein in being soluble in free acids. A pellicle 

 of fat on the surface of urine may sometimes be mistaken for 

 kystein : films of this nature are very thin and usually irides- 

 cent, and the microscope reveals the presence of numerous 

 fat-globules. 



The membrane formed on the surface of urine six or eight 

 days after emission, usually consists of a species of mould ; under 

 the microscope there may be seen innumerable filaments matted 

 together, and interspersed with sporules. 



I once observed a pellicle on the surface of a man's urine 

 three days after emission, which both in chemical and micro- 

 scopical characters presented the closest analogy to kystein. 1 



[Lehmann 2 frequently examined the urine of a pregnant 

 woman from the second to the seventh month. It was of a 

 dirty yellow colour, and more inclined to froth than usual ; it 

 generally became turbid in from two to six hours ; but the morn- 

 ing urine, after standing for thirty-six or forty-eight hours, was 

 always covered with a grayish-white film, which often, in two 

 or three days, sank and mixed with the sediment that formed 

 when the turbidity appeared, but sometimes was a longer period 

 before it broke up. By means of ether he could always re- 

 move from this film a considerable quantity of viscid fat, which 

 formed a soap 'with potash, and then, on the addition of sul- 

 phuric acid, developed a well-marked odour of butyric acid. 

 On treating a large quantity of this urine with sulphuric acid, 

 and distilling, he obtained, after treating the distillate with 

 baryta water, brilliant crystals of butyrate of baryta. The 

 substance taken up by ether, when gently evaporated with nitric 

 acid and exposed to the vapour of ammonia, was not in the 

 least reddened; with concentrated hydrochloric acid, on the 



1 [A similar appearance has been observed by Prout in the urine of a delicate 

 child, fed chiefly on milk. (On Stomach and Renal Diseases, 4th edit. p. 555, note.)] 



2 Lehrbuch der physiologischen Chemie, vol. 1, p. 252. 



