MUSCULAR TISSUE. 247 



(b) W 'eider s Reaction. By gently heating bring the remain- 

 der of the xanthine crystals or residue into solution in bromine- 

 water. Evaporate the solution to dryness on a water-bath. Re- 

 move the stopper from an ammonia bottle and by blowing across 



FIG. 80. 



XANTHINE SILVER NITRATE. 



the mouth of the bottle direct the fumes of ammonia so that they 

 come in contact with the dry residue. Under these conditions the 

 presence of xanthine is shown by the residue assuming a red color. 

 A somewhat brighter color may be obtained by using a trace of 

 nitric acid with the bromine-water. By the use of this modification 

 however we may get a positive reaction with bodies other than 

 xanthine. 



HURTHLE'S EXPERIMENT. 



Tease a very small piece of frog's muscle on a microscopical slide. 

 Expose the slide to ammonia vapor for a few moments, then ad- 

 just a cover glass and examine the muscle fibers under the micro- 

 scope. Note the large number of crystals of ammonium magnesium 

 phosphate, 



NH 4 -0 



Mg-O-P 

 \/ 

 



distributed everywhere throughout the muscle fiber, thus demon- 

 strating the abundance of phosphates and magnesium in the muscle 

 (Fig. 96, page 301). 



