104 PRACTICAL PHYSIOLOGY. [XVL 



(a.) It is a soft doughy indistinctly crystalline body. Place a little under 

 a microscope, add a drop of water, and observe the oil-like drops assuminj 

 worm-like forms, so-called "myelin-fornis." 



{b.) Heat some on platinum, either alone or with sodic carbonate and 

 potassic nitrate = a residue, strongly acid, in which phosphoric acid is readily 

 detected. 



(c.) Action on Polarised Light. — Examine a little under a polarisation 

 microscope. With crossed Nicol's each granule of the substance shows a 

 dark cross on a white ground, just like starch {Dastre). 



4. GlycocoU.— C | ^|^ CO. OH \ _ c.^HjNOo or amido-acetic acid. 



Preparation. — Boil i part of hippuric acid with 4 parts of dilute sulphuric 

 acid (i : 6 water) for ten to twelve hours in connection with a condenser. 

 Carefully pour the mass into a capsule and let it stand for twenty-four hours. 

 Filter, wash the benzoic acid in the filter with cold water, concentrate the 

 filtrate by evaporation, and free it from the last traces of benzoic acid by 

 shaking it with ether. Dilute strongly the acid solution, and neutralise it 

 exactly with baryta water. Allow the precipitate to subside, decant, wash 

 the precipitate with warm water, again concentrate the filtrate until crystals 

 begin to separate on its surface. Allow it to stand twenty-four hours, pour 

 off the mother-liquid, and again evaporate the latter until other crystals are 

 formed. The crystals are recrystallised from water. 



GlycocoU forms clear colourless crystals, with a sweet taste, readily soluble 

 in water, and insoluble in alcohol. 



5. Guanin Reaction. — Guanin occurs in very considerable quantity in the 

 skin of fishes and frogs. Heat a small piece of the skin fi'om the belly of a 

 frog, and heat it on a porcelain capsule with HNO^ as for the murexide test 

 (p. 128). Add caustic soda = orange to cherry-red colour. There is no re- 

 action with ammonia. If there be very little guanin, add dilute caustic 

 potash, and blow on the stain to cool it, when the latter will pass through 

 several nuances from blue to orange. 



6. Nucleo- Albumin, called " tissue-fibrinogen " by Wooldridge, is best pre- 

 pared by Halliburton's method. 



Sodium Chloride Method, — The finely divided thymus gland is ground up 

 in a mortar with an equal volume of sodium chloride. The viscous mass, on 

 being poured into excess of distilled water, forms stringy masses which rise to 

 the surface. Collect and dissolve these in i per cent, sodium carbonate 

 solution. A few cc. of a clear filtered solution injected into the blood-vessels 

 of a rabbit produce extensive intra - vascular clotting, especially in the 

 veins. 



LESSON XVI. 

 THE URINE. 



1. Urine is a transparent liglit-straw or amber-coloured watery 

 secretion derived from the kidneys, containing nitrogenous or 

 azotised matters, salts, and gases. The most abundant constituents 

 are water, urea, and sodium chloride. It has a peculiar odour, bitter 

 saltish taste, and acid reaction. 



