1824.] Active Potter of Dilatation of the Heart. 181 



its older strata ; and it appears to me that a much greater 

 approach towards the same variety of testaceous animals which 

 now inhabits our seas is to be found in the adjoining bed of 

 lower oolite. 



The foregoing observations are confined chiefly to British 

 fossils ; for as a few of the testaceous Cephalopodes still live in 

 the warmer climates, it is possible that the Ammonites, as well 

 as some others of the extinct genera, may have existed longer, 

 and that their remains may be found in the tertiary formations 

 of the more southern latitudes. Although fossil Nautilidae are 

 common in the secondary strata of the United States, they are 

 said not to have been found in South America; and it may, 

 therefore, be queried whether the Cephalopodes were not con- 

 fined to the more northern latitudes when the chalk formation 

 was completed, and whether a decrease in the earth's tempera- 

 ture at that period may not have occasioned the entire destruc- 

 tion of some genera, and a migration of others to the southward. 



It is highly probable, when a more perfect knowledge of the 

 testaceous animals has been obtained, that the line of inquiry 

 which I have now suggested may be greatly extended, and the 

 collected tendency of such analogies between the habits of living 

 animals and the organic remains of the different strata, may 

 serve to throw some light on the nature of the changes which 

 the surface of our planet has undergone. 



Article VI. 



On the active Power of Dilatation of the Heart* 

 By David Williams, M.D. 



(To the Editor of the Annah of Philosophy.) 



DEAR .SIR, Liverpool, Feb. 7, 1824. 



The following observations were made during my experiments 

 on the practicability of an operation for phthisis pulmonalis/|- 

 and also while inquiring into the cause and the effects of an 

 obstruction of the blood in the lungs.'!' By securing the trachea 

 of an animal at the acme of inspiration, the heart continues its 

 action for some time. To ascertain the strength of the active 

 power of dilatation attributed to the right auricle and ventricle, 



* Extracted from An Essay on the Motive Powers of the Circulation of the Blooil, 

 read before the Literary and Philosophical Society of Liverpool, Jan. 182 1. 

 ■f Annul* for June. 

 \ Anmih for September. 



