CHEMISTRY. 



141 



Chemical 

 Examina- 

 tion of 

 Xature. 



a rigid chemical ai.alysis. But from the properties which 

 have been observed, they appear to have a closer resem- 

 blance to the skin than to any other animal substance. 



1. The membranes are thin semitransparent bodies, 

 which envelope certain parts of the body, especially the 

 viscera ; such as, the dura and pia mater, the plura, the 

 peritoneum, the periosteum, &c. These substances are 

 soft and pliable ; when macerated in water, they swell, 

 and become somewhat pulpy ; and by continued decoc- 

 tion in hot water they are almost completely dissolved, 

 and the solution concretes into gelatine. They are con- 

 vertible, of course, into the same substance as the cutis 

 by decoction ; hence we must consider their composition 

 as similar. Like hides, they may also be tanned and con- 

 verted into leather. From the experiments of Mr Hat- 

 chett, it appears that they contain no phosphate of lime 

 as a constituent part, and scarcely any saline ingredients ; 

 for when calcined, they leave but a very inconsiderable 

 residuum. Thus 250 grains of hog's bladder left only 

 0.02 grain of residuum. 



2. The tendons are strong, pearl-coloured, brilliant 

 bodies, which terminate the muscles, and attach them to 

 the bones, and are known in common language by the 

 name of sinews. When boiled, they assume the form of 

 a semitransparent gelatinous substance, of a pleasant taste, 

 well known in boiled meat. If the decoction be con- 

 tinued, they dissolve completely, and are converted into 

 gelatine. From these facts we are authorised to con- 

 clude, that the composition of the tendons is similar to 

 that of the membranes and cutis. 



3. The ligaments are strong bands which bind the 

 bones together at the different joints : they are fibrous 

 substances, very dense and strong, and somewhat elas- 

 tic. When boiled, they yield a portion of gelatine, but 

 they resist the action of water with great obstinacy, and 

 after a great deal of boiling retain their form, and even 

 their strength. The ligaments, then, differ essentially 

 from the two last species. How far they resemble coa- 

 gulated albumen, remains to be ascertained. It is not un- 

 likely that they will form a genus apart. 



4. The glands are a set of bodies employed to form 

 or to alter the different liquids which are employed for 

 different purposes in the animal body. There are two 

 tets of them : the conglobate, which are small, scatter- 

 ed in the course of the lymphatics ; and the conglome- 

 rate, such as the liver, kidneys, &c. Fourcroy gup- 

 poses the first of these to be composed of gelatine ; but 

 this is not very probable. The structure of the large 

 glands has been examined by anatomists with great care; 

 but we are still ignorant of their composition. Indeed, 

 the present state of chemistry scarcely admits of an ac- 

 curate analysis of these complicated bodies. 



SECT. VI. Of the Brain and Nerve*. 



The brain and nerves are the instruments of sensation, 

 and even of motion ; for an animal loses the power of 

 moving a part the instant that the nerves which enter it 

 are cut. 



The brain and nerves have a strong resemblance to 

 each other ; and it is probable that they agree also in 

 their composition. But hitherto no attempt has been 

 made to analyze the nerves. The only chemists who 

 have examined the nature of brain are Mr Thouret and 

 Mr Fourcroy. 



The brain consists of two substances, which differ 

 from each other somewhat in colour, but which, in other 

 respect*, seem to be of the same nature. The outermost 



matter, having some small resemblance in colour to wood- Chemital 

 ashes, has been called the cineritious part ; the innermost f^~ 

 has been called the medullary part. Nturc. 



Brain has a soft feel, not unlike that of soap ; its tex- >~ Y ~' 

 ture appears to be very close ; its specific gravity is great- Properties 

 er than that of water. of brain - 



When brain is triturated in a mortar with diluted sul- 

 phuric acid, part is dissolved ; the rest may be separat- 

 ed by filtration in the form of a coagulum. The acid 

 liquor is colourless. By evaporation, the liquid becomes 

 black, sulphurous acid is exhaled, and crystals appear ; 

 and when evaporated to dryness, a black mass remains 

 behind. When this mass is diluted with water, a quan- 

 tity of charcoal separates, and the water remains clear : 

 The brain is completely decomposed, a quantity of am- 

 monia combines with the acid, and forms sulphate of 

 ammonia, while charcoal is precipitated. The water, 

 by evaporation and treatment with alcohol, yields sul- 

 phates of ammonia and lime, phosphoric acid, and 

 phosphates of soda and ammonia. Brain, therefore, 

 contains 



Phosphate of lime, 

 Phosphate of soda, 

 Phosphate of ammonia. 



Traces also of sulphate of lime can be discovered in it. 

 The quantity of these salts is very small ; altogether they 

 do not amount to , J :r th part. 



Diluted nitric acid, when triturated with brain, like- 

 wise dissolves a part, and coagulates the rest. The so- 

 lution is transparent. When evaporated till the acid be- 

 comes concentrated, carbonic acid gas and nitrous gas 

 are disengaged ; an effervescence takes places, white 

 fumes appear, an immense quantity of ammonia is dis- 

 engaged, a bulky charcoal remains, mixed with a con- 

 siderable quantity of oxalic acid. 



When brain is gradually evaporated to dryness by the 

 heat of a water bath, a portion of transparent liquid se- 

 parates at first from the rest, and the residuum, when 

 nearly dry, acquires a brown colour ; its weight amounts 

 to about one-fourth of the fresh brain. It may still be 

 formed into an emulsion with water, but very soon sepa- 

 rates again spontaneously. 



When alcohol is repeatedly boiled upon this dried re- 

 siduum, till it ceases to have any more action, it dissolves 

 about five eighths of the whole. When this alcohol cools, 

 it deposites a yellowish white substance, composed or 

 brilliant plates. When kneaded together by the fingers, 

 it assumes the appearance of a ductile paste : at the 

 temperature of boiling water it becomes soft, and when 

 the heat is increased it blackens, exhales empyreumatic 

 and ammoniacal fumes, and leaves behind it a charry 

 matter. When the alcohol is evaporated, it deposites a 

 yellowish black matter, which reddens paper tinged with 

 turnsole, and readily diffuses itself through water. 



Pure concentrated potash dissolves brain, disengaging 

 a great quantity of ammonia. 



SECT. VII. Marrow. 



The hollows of the long bones are in living animals Marrow, 

 filled with a peculiar species of fat matter, to which the 

 name of marrotv has been given. In some bones this 

 matter is a good deal mixed with blood, and has a red 

 colur ; in others, as the thigh bones, it is purer, and 

 has a yellow colour. Various experiments on this mat- 

 ter were made by the older chemists, showing it to be 

 analogous to animal fats, and pointing out some of its 

 peculiarities. Berzelius has lately examined it in detail, 



