BRAIN. 89 



free phosphoric acid present in it. Observe that it 

 contains 1*74% of ash, of nearly the following com- 

 position : 



Acid potassium phosphate 55'24 



sodium 22'93 



iron 1-23 



calcium 1-62 



magnesium 3'40 



Free phosphoric acid 9-15 



Sodium chloride 4*74 



Potassium sulphate 1'64 



Silica... 0-42 



100-37 



17. Burn another portion very gradually, adding 

 hot saturated baryta water to the charring and charred 

 matters from time to time, in order to neutralise the 

 free phosphoric acid formed by the destruction of 

 lecithine, and preserve the whole of the chlorides and 

 sulphates intact. Prove by comparison that the acid 

 phosphates found by process 16 are mainly formed by 

 the phosphoric acid from the lecithine, expelling 

 chlorine and sulphuric acid from the glowing ash. 



18. Burn some dry white brain-matter, and notice 

 that it leaves about 1*72% of ash containing free phos- 

 phoric acid and a large amount of acid phosphates. 



19. Burn some dry gray brain-matter, and notice 

 that the quantity of its ash is only 1*16 %, that it is 

 alkaline, and contains a much smaller quantity of 

 phosphates than the ash from white matter. 



20. Treat a minute fibre of brain-substance or a 

 bundle of nerve-fibres under the microscope with 

 perosmic acid, and notice a blue reaction, 



