On the Case of Miss Margaret MacAuoij. 45 



liioh state of irritability in the iievvoiis system ; in consequence 

 of which, so far from wondering at the publication of a case some- 

 what analogous in a human being, my astonishment has often 

 been excited, that in the enlarged practice and advanced state of 

 medical and anatomical knowledge, no instances have before been 

 ])roduced which could throw light upon so interesting a subject. 

 Now, in reading Dr. Renwick's statement, it struck me that 

 the same theory by which I had endeavoured to account for the 

 powers of animals and insects might be applicable to the case in 

 question ; namely, the action or influence of caloric. We know 

 that by the intervention of a prism the solar rays are divided into 

 their calorific, colorific and deoxidizing proportions. It will be 

 readily admitted that the calorific division would probably have 

 the greatest influence upon nerves rendered unusually sensible by 

 disease or otlier cause ; and such in the case of Miss MacAvoy 

 appears to be the fact. I proceed to an illustration : — Dr. Her- 

 schel's experiments prove that the most refrangible rays have the 

 least heating power ; and that the heating power gradually in- 

 creases as its refrangibility diminishes ; the violet ray has there- 

 fore the smallest heating power, and the red ray the greatest], 

 accordingly the effect of the red ray ought to be much stronger 

 upon an irritable nerve than the violet which terminates the ca- 

 lorific division. On referring to Dr. Renwick's account there 

 is evidence that such is the fact. Page 59. July 25, " She told a 

 scarlet coloured cloth upon the back of her hand uncovered, but 

 she could not tell any other colour given her." Page 61, The red 

 and orange rays of the solar spectrum being thrown by a prism 

 upon her hand, she said it appeared like gold. She felt the 

 spectrum ivarm. Theviolet rays were the least pleasant. PagelOD, 

 '•' I prefer the brighter colours as they give a pleasurable feeling, 

 a sort of glow to mv fingers, and indeed all through me. Black 

 gives me rather a shuddering feeling." Again : we know that 

 metals are the best conductors of caloric, but in very different 

 proportions; according to Dr. Ingenhousz, they are classed in 

 she following order: — Silver, gold; tin, copper, nearly equal. 

 Platinum, iron, steel, lead, all much inferior to the others. If a 

 more rapid action of caloric can therefore be supposed to have 

 a more sensible effect than a slower. Miss MacAvoy ought in 

 the above order to be susceptible to metallic impressions, and we 

 find she is so most accurately. P. 63, " The silver of a watch- 

 case {c\t Jiner than the gold of the seal ; but gold and silver had 

 a much Jirier feel than steel or brass." In p. 109, her reply to 

 the question. What is the feeling you have of different me- 

 tals? she repeats the remark: " I feel gold and silver to be 

 more pleasant than brass, copper, or steel." I have already re- 

 ferred 



