4. Extract cerebrine and protagon with boiling alcohol, as directed under those bodies.

5. From the cold ether extract containing cholesterine and lecithine which is obtained in the preparation of cerebric acid, lecithine is isolated by the process given under that substance, any great excess of the platinic or cadmium chloride being avoided. The nitrate from the precipitated lecithine compound is boiled with excess of plumbic hydrate and filtered. On cooling a copious crystalline deposit will form, from which pure cholesterine may be obtained by recrystallisation from boiling alcohol.

6. Rub brain-matter in a mortar with water containing enough sodium chloride to prevent cerebrine and cerebric acid from forming an emulsion; filter the mixture. The clear filtrate will contain potassiumalbumen or casein, which may be precipitated by sulphuric acid not in excess. From the filtrate addition of a few drops of acetic acid and boiling will throw down albumen if present.

7. Rub in a mortar to a thin milk with excess of baryta water, heat till just coagulated, filter, remove the main bulk of the baryta from the filtrate by a current of carbonic acid, and the last traces by exact precipitation with sulphuric acid and evaporate to a low bulk. Divide this extract into two portions.

8. One portion of the extract distil with dilute sulphuric acid to obtain the volatile acids, acetic and formic. Examine them as directed under those bodies.

9. The other portion of the extract heat with ether slightly acidified with sulphuric acid. Mix the ethereal solution with water, distil off the ether, remove any sulphuric acid by cautious addition of baryta water, evaporate the filtrate and test for lactic acid {q. v) by the zinc salt, and for urea.

10. The part insoluble in ether must be diluted with water, freed from sulphuric acid by addition of just sufficient baryta water, the filtrate evaporated to a low bulk and exhausted with boiling absolute alcohol. Leucine, kreatine, and urea will dissolve, and some leucine may crystallise out on cooling. From the alcoholic solution expel the alcohol by distillation till the aqueous residue forms not too thick a syrup, adding a little water, if necessary, and set aside to crystallise. Kreatine and leucine will separate while urea will remain in the mother liquor, and may be isolated by nitric or oxalic acid. (See Urea).

11. The kreatine and leucine may sometimes be mechanically separated (the former being in crystals, the latter in opaque granules) and afterwards be purified by crystallisation from alcohol. If not, dissolve the mixed deposit in hot water, and boil with zinc chloride. On cooling and standing, kreatinine, zinc chloride, and kreatine will separate in granules (see those bodies). From the liquid after precipitation of the zinc with ammonium carbonate and boiling, and evaporation of the filtrate, leucine (and homologues) may be isolated by the process given under leucine {a. v.).

12. The portion insoluble in boiling alcohol must be exhausted with boiling water. Some uric acid may remain undissolved. To the boiling solution add neutral acetate as long as any precipitate is produced. Filter.

13. The precipitate may contain lead urate as well as lead, salts of inosic and similar acids. Suspend in a moderate quantity of water and decompose by sulphuretted hydrogen. The lead sulphide will retain most of the uric acid, which may be extracted by boiling with water, while the filtrate will contain the inosic acid and allied bodies, if present.

14. The filtrate from the precipitate by neutral lead acetate must be precipitated by basic lead acetate and cupric acetate. The solution filtered from these precipitates may contain tyrosine, which must be identified by evaporating, dissolving the crystals or deposit in a little hydrochloric acid, precipitating by sodium acetate, and applying the mercury nitrate and nitrite test. (See Tyrosine).

15. The precipitate may contain xanthine, hypoxanthine, and inosite. Suspend the precipitate in a rather large quantity of water, decompose by hydrothion, filter, extract the lead sulphide with boiling water and evaporate the filtrate and extract together to dryness. From the residue extract the inosite by cold water, and purify by crystallisation. The remaining xanthine and hypoxanthine may be separated and purified by the processes described under those bodies.

16. Burn a portion of dried mixed brain-matter carefully in a platinum dish (best in a muffle) and analyse the ash, noticing that there is always a quantity of free phosphoric acid present in it. Observe that it contains 1*74 % of ash, of nearly the following composition:

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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 phosphoric 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.

21. Search for amyloid matter by the process described under that body.

22. In some diseases, such as softening of the brain, search iorfree glycero-phosphoric acid. This -will pass into the liquids obtained by sodium chloride, process 6, and by baryta water, process 7. The sodium chloride solution, freed from caseine and albumen, as above, must be filtered, neutralised with calcium carbonate, evaporated to a small compass, and precipitated boiling with a sufficient volume of alcohol. Dissolve the precipitate in as little cold water as possible, and boil; calcium glycerophosphate will separate, and must be again dissolved and thrown down by boiling, finally washed with a very little hot water, then with alcohol, dried at 100° C, and analysed. It should contain 60-47 % of Ca.

23. To obtain glycero-phosphoric acid from the baryta water extract, process 7, take the mother liquor of kreatine and leucine, remove urea by oxalic acid, and subject the residual fluid to the treatment described in the previous paragraph.

24. The albuminous matters which remain insoluble in the course of any of the processes of extraction above described, will yield by chemolysis (e. g., by boiling with dilute sulphuric acid) leucine, tyrosine, and the other usual decomposition products of albumen.

Butyric acid.—1. Produce butyric acid from sugar,* as directed under lactic acid, but allow the mixture to stand five or six weeks. The calcium lactate is

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