Of the Physiology of certain Disorders of Health. 1 29 



tlinar}- law of refraction, as Huygeiis and Newton supposed, or 

 is produced by forces dependent on the elementary structure of 

 the crystal, is a question which still remains to be determined. 

 The extraordinary reflection and refraction arising from the last 

 of these causes, winch I have discovered in mother of pearl*, 

 present an analogy, by no means remote, to the phagnoniena of 

 double refraction. 



XXIII. Of the Physiology of certain Disorders of Health 

 founded on a Knowledge of the proportionate Development 

 and Functions of the special Organs of the Mind, By 

 Thomas Forster, Esq. 



To Mr. Tilloch. 



Sir, — In a former paper I endeavqured to point out some of 

 the practical applications of the new discoveries into tlie struc- 

 ture and functions of the brain, with a view to show the various 

 means in which it might become useful to society. For I consi- 

 der every inquiry as to the particular utility of any science to be 

 merged in the general question. Whether or no it be the illus- 

 tration of truth? Yet it is of use'to particularize the special pur- 

 poses for which it may be employed. I proceed to mention 

 briefly a few curious facts relative to the history of certain kinds 

 of aberration of mind, and to their connexion with particular 

 organization. 



It seems to me, that we cannot obtain any accurate knowledge 

 of the nature of this mental disorder, till we have first becoii;e 

 acquainted with the mind in its healthy state. Insanity consist-s 

 in the erroneous or inordinate energy of the functions of the mind 

 in general, or of some of the faculties in particular. To learn 

 the physiological history of these, we must previously know what 

 are the primitive faculties of the mind in a healthy condition; 

 ^ve must first know the passions, learn what are the results of 

 primitive and uncompounded organs, and what are compounded 



* This substance, whose remarkable optical properties T have explained 

 ill another place, resembles the ngate, the carbonate of barytes, and the 

 iiitiatc and carbonate of potash, in jiivins; a bright and a nebulous iniatriJ, 

 wiien the liizlit is transmitted in one diiection, and twobri^iht in)ai;es, when 

 the lij^ht is transmitted in anotlier direction; but it possesses thi-> property 

 under circumstances of such an extraordinary nature, that I coiiid not with 

 propriety have introduced any account of it into this paper. 



A numlier of soft substances, of animal and ve^elahlif origin, have like- 

 wise tli€ faculty of formiui; a bright and a nebulous image, under various 

 singular moditicntions. A full account of the results which 1 have obtained 

 \\\t\\ this class of sidistauces, will l)0 found in another paper. 



Vol. 4a. No. 202. iV^. 1815. 1 of 



