l82 



NATURE 



\yan. 6, 1876 



810 to 1,500 years, the yew from 1,214 to 2,820, and the 

 Baobab {Adansonia digitatd) to 5,coo years, the author 

 points out that these figures have been based upon the 

 general assumption of each concentric ring of wood being 

 the growth of one year. Speaking of his own experience, he 

 says : — "I have carefully examined and counted the annual 

 layers of a great many specimens — taking generally the 

 average of the trees— with theview to showthe common and 

 comparative rates of growth, and have tabulated them to 

 afford an opportunity of noticing any variations there 

 may have been in the time required to form the wood in 

 each of the several given diameters of 6, 12, 18 inches," 

 &c. In these tables it is shown that in fifteen specimens 

 of oak, the diameter of whose stems were in all cases 

 6 inches, the number of rings ranged from 12 to 49 ; in 

 the same number of sections measuring 12 inches dia- 

 meter they ranged from 19 to 105, and in those of 18 

 inches diameter from 24 to 160. In sections 'of Green- 

 heart {Nectandra Rodicei) of 6, 12, and 18 inches diameter, 

 the concentric rings were respectively 37, 60, and 83, 

 while in Mexican mahogany of the same dimensions the 

 result showed the number of rings at 17, 30, and 44. . In 

 most cases from six to ten sections were examined, and 

 the average so obtained. 



In the matter of ordinary timber the information given 

 is varied and tolerably complete, and the opinions of the 

 author as regards strength, durability, and value for prac- 

 tical purposes may, of course, be taken as the opinion of 

 one having experience and authority to speak on such 

 matters. Moreover, the tables showing the breaking 

 weights of the different woods and their specific gravities 

 are the results of actual experiments. It is much to be 

 regretted that in a work of this kind, which has not been 

 produced without some care, more attention has not been 

 given to scientific accuracy, not only in tracing out the 

 sources of the woods mentioned, but also in bringing 

 what botanical nomenclature has been attempted down 

 to modern times. Thus, for instance, the " Magaran 

 duba" of Brazil (p. 182) might have been accredited as 

 being a species of Mivmsops, the " Cedro," on the follow- 

 ing page, not as a species of " Cedar " but of Cedrela 

 {Cedrela odorata probably), and the " VinhaticoV' (p. 186) 

 probably Persea indica. Again, with regard to African 

 oak or teak, it is stated to be " probably the Swietenia 

 senegalensis or S. Khaya" but it is well known that the 

 durable timber commonly known under the above names 

 is produced by Oldfieldia africana, a Euphorbiaceous 

 tree. The Cuban Sabicu wood, likewise, of which the 

 stairs of the great Exhibition building in Hyde Park in 

 1 85 1 were constructed, and which, we believe, are still in 

 use at Sydenham — such is the durability of the wood — is 

 described as being produced by Acacia formosa, but it is 

 under Lysiloma sabicu that any description of this wood 

 is to be found in works of a botanical character. 



It is not with the view of depreciating the value of the 

 book that we point out these errors. In a new edition, 

 with the aid of a botanist and a determination to extend 

 the scope of the work so as to include all woods known 

 in commerce, the value of the book might be considerably 

 enhanced. As it is, however, besides the technical details 

 there are numerous interesting facts distributed through 

 its pages, many of which are new to^us. 



John R. Jackson 



RECENT FRENCH EXPERIMENTAL 

 PHYSIOLOGY* 



Physiologie Experimentale. Travaux du Laboratoire de 

 M. Marey. (Paris : G. Masson, 1876.) 



THE second of the memoirs in the work before us, by 

 M. Marey, contains the description of a new 

 schema, or dynamical model of the circulatory system, 

 which from the ingenuity of its construction calls for 

 special notice. 



M. Marey, not satisfied with the original attempt of 

 Weber to reproduce the phenomena of the circulation in 

 a system of elastic tubes, nor with his own earlier efforts 

 in the same direction, was led to the construction of the 

 one to be noticed immediately. He tells us that all pre- 

 vious models were correct enough in imitating certain 

 special points in the vascular circulation, but these were 

 at the expense of, and to the total neglect of, others. The 

 perfect reproduction of each phase is the end he has had 

 in view in the construction of the new apparatus. 



It can be proved without doubt that the heart takes a 

 longer time to relax than to contract ; the systolic curve, 

 when represented graphically, is therefore more abrupt 

 than the diastolic. To represent this on paper mechani- 

 cally, the easiest method is by the employment of a cam 

 or eccentric, which, as it turns, lifts a lever resting upon 

 it and following the variation in its eccentricity. 



In Fig. I the winch handle turns an axle on which 

 two cams are fixed, the whole being connected with the 

 two steady-arms and the immovable upright board on 

 the left-hand side. A flywheel tends to render the rota- 

 tion of the axle uniform. The irregularly-shaped eccen- 

 trics (c.v. and CO.), the form of which will be explained 

 further on, each move one of the smaller boards to the 

 right of the figure, because these are pressed towards 

 the left by the elastic spring F, and the dilatation of the 

 cavities of the artificial heart (v and o), whilst they 

 are being refilled. They transmit their movements 

 through the intervention of the fixed pulleys attached to 

 the boards, which latter again act on the artificial heart 

 by the strain they exercise upon the cords s.O. and S.v. 

 The action of the auricle being intermittent, the machine 

 is so arranged that the cord S.O. is lax (as in the figure) 

 during the time that it is at perfect rest. The ventricle 

 never being in a state of true repose, but always in a 

 state of contraction or expansion, it does not require the 

 extra apparatus. 



The artificial heart is constructed with caoutchouc cavi- 

 ties, supphed with valves to represent those in the human 

 circulation. The auricle is covered with netting, to which 

 four parallel cords, running through holes in the big 

 board, are attached. The cords are fixed on a square 

 piece of wood, which is kept in position by a spiral spring, 

 and in connection with the moving board by the thread 

 S.O. The ventricle has over it a case (white in the figure) 

 to the edges of which cords are fixed, which are attached 

 at their other ends to a board, which is put into commu- 

 nication with the moving board by means of the hooks 

 and elastic rings (f), and the cord S.v. It is evident that 

 any strain on the cords s.v. or S.O. will compress the 

 auricle (o) and the ventricle (v) against the main board 

 to which they are attached, and so produce a systole of 



* Continued Irom p. 146. 



