530 Miscellaneous. 



analogous substance, the plant may continue to live, though in less 

 perfect health. Thus potash may be to a certain extent replaced by 

 soda, and, as has been observed in certain samples of tobacco, even 

 by lime. In the case of the grape, no rotation of crops is possible, 

 and the probability of exhaustion is therefore so much the greater. 

 The juice of the grape is very rich in potash, which is deposited, on 

 standing, in the form of crude tartar. This potash is not returned 

 to the soil, but is consumed for manufacturing purposes. AA ithout 

 having had the opportunity of pro^^ng this view by analysis, I am of 

 opinion that the soil of old vineyards will be found deficient in pot- 

 ash. As a means of remedying this defect, I suggest that granite 

 should be heated to redness, plunged in water, and ground to powder. 

 Let this be well mixed with about half its weight of lime, and the 

 mass be exposed for some time to the action of the atmosphere. 

 This compost may then be sparingly applied as a manure to the vines. 



J, W. Slater. 



On the Cause of the Rhythmic Motion of the Heart. 

 By James Paget, Esq., F.R.S. 



The author draws the following conclusions as to the most pro- 

 bable explanation of the rhythmic action of the heart : — 



1. In the Yertebrata it is due to the time-regulated discharges of 

 nerve-force in certain of the ganglia in and near the substance of the 

 heart, by which discharges the muscular walls are excited to con- 

 traction. 



2. In Invertebrate, the corresponding pulsatile movements of 

 hearts or vessels are probably independent of nerve-force. 



3. The time-regulated rhythmic action, whether of the nervous 

 centres or of the independent contractile walls, is due to their nutri- 

 tion being rhythmic, i. e. to their being, in certain periods, by nutri- 

 tive changes of composition, raised, with regulated progress, to a 

 state of instability of composition, in their decline from which they 

 discharge nerve-force, or change their shape, contracting. 



4. The muscular substance of the heart in the "N'ertebrata, governed 

 in its rhythmic action by appropriate nervous centres, has a 

 rhythmic nutrition of its own, corresponding and coordinate with 

 theirs ; the impairments of its structure during action being repaired 

 in repose. 



5. Rhythmic nutrition is a process in accordance with the general 

 laws of organic life, very many organic processes being composed of 

 timely-regulated alternate action and inaction, or alternate opposite 

 actions, i. e. being rhythmical, with larger or shorter xu^,its of time ; 

 and all organic processes being chronometric, i. e. ordered according 

 to laws of time as exact, and only as much influenced by external 

 conditions, as are those relating to weight, size, shape, and com- 

 position. — Proc. of Hoy. Hoc. May 28, 1857. 



