8 



when forcibly compressed between two plates of glass, it also exhi- 

 bited beautiful colours, that were complementary to each other in 

 the two images of a candle seen through it, by means of a prism of 

 Iceland spar; and when the pressure was removed, these complemen- 

 tary tints disappeared. 



Inasmuch as these colours might be supposed owing to the thin- 

 ness to which the plate of jelly was reduced by pressure, Dr. Brewster 

 cut the cake to the same thinness which it had possessed while under 

 compression, but without any production of colours till pressure was 

 again applied. 



In the author's concluding experiment, he formed one twentieth 

 of an inch thick of the same jelly, by melting it between two plates 

 of glass. When merely consolidated by cooling, this had no power 

 of depolarization ; but by pressure it instantly restored the evanescent 

 image, and exhibited, as in the former cases, the complementary co- 

 lours, showing, says the author, that pressure communicates a modi- 

 fication of structure correspondent to that of crystallized minerals. 



Experiments made with a View to ascertain the Principle on which the 

 Action of the Heart depends, and the Relation which subsists between 

 that Organ and the nervous System. By A. P. Wilson Philip, Phy- 

 sician in Worcester. Communicated by Andrew Knight, Esq. F.R.S. 

 Read February 9, 1815. [Phil. Trans. 1815,^. 65.] 



The author's ultimate object is to ascertain the manner in which 

 certain poisons act in destroying life ; but for this purpose he found 

 it necessary previously to determine how far the powers of the ner- 

 vous and sanguiferous systems depend on each other ; and though it 

 be generally allowed that the powers of the nervous system cannot 

 continue long after the cessation of the circulation of the blood, the 

 converse is not so generally admitted ; since there are persons who 

 maintain that the nervous power may be wholly destroyed without 

 impairing the vigour of the heart. 



The present inquiry relates solely to this part of the subject, how 

 far the power of the heart is influenced by the state of the nervous 

 system ; and the author designs, at some future time, to investigate 

 experimentally, by what steps certain poisons destroy the powers of 

 both. 



M. Le Gallois maintains, that though the destruction of the brain 

 does not impair the action of the heart, it is immediately and ex- 

 tremely debilitated by destruction of the cervical part of the spinal 

 marrow. Dr. Philip, however, did not find this to be the case in his 

 experiments, of which the first ten, performed on rabbits, relate al- 

 most exclusively to the effect of destroying the spinal marrow. 



The animals were in general first rendered insensible by a blow on 

 the occiput, after which the circulation was found to depend wholly 

 on the continuance of respiration by artificial means, and not to be 

 in any degree altered by subsequent removal or destruction of the 

 spinal marrow, which was effectually done by means of a hot wire. 



