EYE 



matter requires no other mordant than oxygen to fix it on 



'^°ii!when diftiUed, extraaive yields an acid liquid 

 impregnated with ammonia. „ „, ^ , t 



It cannot be doubted, continues Dr. Thomfon, that there 

 are many different fpecies of extraaive matter, thougli the 

 difficulty of obtaining each feparately has prevented che- 

 mifts from afcertaining their nature withprecifion. Watery 

 extraas, when obtained by flow evaporation to drynefs, 

 always have an acid taite, and redden litmus. They all 

 vield a precipitate while Hquid on the addition of ammonia. 

 This precipitate is a compound of hme and mfoluble ex- 

 traaive. Lime always caufes them to exhale the odour of 

 ammonia. It has been afcertained, that the extraaive prin- 

 ciple is more abundant in plants that have grown to matu- 

 rity than in young plants. 



All the extraas prepared by apothecaries are compounds 

 of the extraaive principle with feveral others, even as many 

 as eight or more, according to Dr. Thomfon. In fhort, 

 this department of vegetable chemiftry is at prefent in a very 

 confufed and imperfeift ftate. 



Vol. XIV. 

 EYE, Phfwlogy of the, col. 6, 1. 26 from bottom, for an 

 inch r. one-tenth of an inch. 



Eye, Humours of. Chemical Properties of. Some experi- 

 ments have been made on thefe fluids, the refults of which 

 deferve to be briefly mentioned. 



Aqueous Humour — Mr. Chenevix found the fp. gr. of 

 the aqueous humour of the flieep at 60° to be 1.009. 

 This fluid fcarcely affeas vegetable blues while frefh. On 

 expofure to heat, a flight coagulum is formed. Tannin 

 occafions a precipitate in it, both before and after boiling. 

 Nitrate of filver likewife produces a precipitate, but no 

 other metallic fait. According to Berzelius, loo parts of 

 it confift of 



Water - - - 98-10 



Albumen, a trace 



Muriates and laaates - 1.15 



Soda with animal matter, foluble ) ^ 

 only in water - - j 



E Y N 



C^flaUine Lens. — The fp. gr. of this is 1. 100. When 

 frefli "it has little tafi;e. It putrefies very rapidly. It is 

 almoft completely foluble in water. The folution is partly 

 coagulable by heat, and gives a copious precipitate with 

 tannin both before and after boiling. According to Ber- 

 zelius, it is compofed of 



Vitreous Humour. — This poflefles very nearly the fame 



properties as the aqueous. Even its fp. gr. is the fame, or 



only a very little heavier. According to Berzelius, it is 



compofed of 



Water - - 98.40 



Albumen - - .16 



Muriates and laaates - 1.42 



Soda with animal matter, foluble 1 



1 „ > .02 



only in water - - j 



Water . . - 



Pecuhar matter 



Muriates, laaates, and animal ) 



matter foluble in alcohol - J 

 Animal matter, foluble only in( 



water, with fome phofphates | 

 Portions of the remaining in-^ 



foluble cellular membrane - j 



58.0 



35-9 



2.4 



1-3 



2.4 



The peculiar matter of the lens poflefles all the chemical 

 properties of the colouring matter of the blood, except 

 colour. 



The humours of the human eye are compofed of the 

 fame ingredients as thofe of the ftieep ; but they differ in 

 their fp. gr. Thus the fp. gr. of the human aqueous and 

 vitreous humour is 1.0053 ' ^^^'^ '^^ ^^^ cryfl;anine 1.0790. 

 The humours of the eyes of oxen alfo refemble thofe of the 

 flieep. The fp. gr. of the aqueous and vitreous humours is 

 1.0088 ; that of the cryftalline 1.0765. The cryitalline of 

 the ox weighed thirty grains. When the whole was pared 

 away, except fix grains in the centre, the fp. gr. was found 

 to be 1. 194. 



Sir H. Davy found the fame confl;ituents in the eyes of 

 birds ; but the fp. gr. of the vitreous humour in thefe 

 animals is greater than the fp. gr. of the cryftalline. 



Pigmentum Nigrum. — This curious fubftance has been 

 examined by Gmehn. From 500 eyes of oxen and calves 

 he coUeaed 75 grains. Its colour is blackifli-brown. It is 

 taftelefs, and adheres to the tongue hke clay. It is info- 

 luble in water, alcohol, ether, oils, lime-water, and acetic 

 acid. It diffblves in potafli and ammonia by the afliftance 

 of heat, and is again precipitated by acids. Sulphuric acid 

 diflblves it, and becomes black. Muriatic acid alfo forms 

 an imperfea folution. Nitric acid diffolves it, and changes 

 its colour to reddifti-brown. When diftiUed it yields water, 

 brown oil, and carbonate of ammonia. The refiduum 

 confifts almoft entirely of charcoal. 



Eye, col. 2, 1.6, r. In the year 181 1, the town and 

 parifli confiifed of 326 houfes, and 1893 inhabitants. 



EYEMOUTH. Add— By the return of 181 1, the 

 parifti contained 115 houfes, and 962 inhabitants. 



EYNSHAM, or ExsHAM, 1. ult — In 181 1, the number 

 of inhabitants was 141 8, and of houfes 246. 



100. 



