226 



pidly as the temperature increased, and at above 100 a portion of the 

 power of the magnet was permanently destroyed. 



In regard to the diurnal changes in the terrestrial intensity, the 

 author's experiments lead him to suggest the following queries for 

 the consideration of those who may have an opportunity of making 

 such observations : Does the time of the minimum intensity corre- 

 spond with the time at which the sun is on the magnetic meridian ? 

 Does the time of maximum intensity correspond to the sun's passing 

 the plane of the equator of the dipping-needle ? Does any change 

 take place in the intensity while the sun is below the horizon ? Are 

 any periodical effects corresponding to the time of rotation of the 

 sun about its axis observable ? Is the diurnal change of intensity at 

 the time of new moon sensibly different from what it is at the time 

 of quadrature ? If the moon do produce an effect on the needle, it is 

 evidently less than that of the sun ; should we then attribute it to 

 solar heat, or to the magnetism of the sun ? 



The Croonian Lecture. On the Existence of Nerves in the Placenta. 

 By Sir Everard Home, Bart. V.P.R.S. Read November 18, 1824. 

 [Phil. Trans. 1825,;?. 66.] 



In this lecture the author makes known his discovery of the ex- 

 istence of nerves, both in the foetal and maternal portions of the pla- 

 centa. His previous researches had led him to doubt the existence 

 of blood-vessels without nerves, and the extreme vascularity of the 

 placenta led him to suspect them in that organ. With the assistance 

 of Mr. Bauer, therefore, he first examined the placenta of the Seal, 

 the arteries and veins of which had been injected, and in which nerves 

 were discovered, not only surrounding the umbilical arteries, but also 

 in the uterine portion. 



In the pregnant uterus of the Tapir of Sumatra, in which, there 

 being no placenta, the umbilical chord is connected with the chorion, 

 the nerves were very conspicuous in the transparent portion of the 

 chorion, along which the branches of the funis pass before they ar- 

 rive at the spongy part. 



Having thus established the existence of nerves in the placenta, 

 and where that is wanting in the flocculent chorion, Sir Everard pro- 

 ceeds to offer some general remarks upon their probable uses and 

 influences. 



From the various sources, the number, and the ganglia of the 

 uterine nerves, and from the circumstance of their becoming enlarged 

 during pregnancy, he infers their powerful influence on the fcetus in 

 utero ; and for the further illustration of this subject, the author adds 

 a description of the nerves connected with the generative organs in 

 the human species, the quadruped, the bird, and the frog. 



He concludes this lecture with remarking, that since the discovery 

 of the placenta! nerves proves the existence of a communication 

 through their medium, between the brain of the child and that of 

 the mother, some light may be thrown on the degree of dependence 



