Vol. XXII. No. 5.] 



POPULAE SOIEl^CE I^EWS. 



77 



iHtUicine anU Pbarmatp. 



MAN AS A STEAM-ENGINE. 



A BKOAD and general distinction may be 

 made between a plant and an animal, in that 

 one is a reducing agent, decomposing carbonic 

 dioxide and water, and building up into its 

 structure various complicated hydrocarbons 

 and nitrogenous bodies, while the action of 

 the animal organism is an oxidizing one, as 

 it takes the substances stored up by the plant, 

 and changes them once more into water and 

 carbonic dioxide. In this process heat and 

 energj- are developed, and in this way man 

 obtains his capacity for action and work ;i while 

 his resemblance to a steam-engine, which pro- 

 duces its power in a mechanical way, albeit 

 by the same oxidizing process, is a very curi- 

 ous one. 



First of all, the engine must have fuel, or 

 some material which is capable of oxidation 

 or combustion. The machine is satisfied with 

 simple carbon, or coal ; but the human organ- 

 ism requires a more complex arrangement of 

 the molecules of carbon and hj-drogen which 

 it is to burn, so it must be fed upon starches, 

 sugars, albuminoids, etc., which are as trul}' 

 l)urned in the human 83Stem as the coal is in 

 the furnace, and in both cases develop heat 

 and power. 



The stomach may be considered as the 

 " fire-box " of the human machine, although, 

 strictly speaking, it is a place where the fuel 

 is prepared for combustion. To state just 

 how and where in the body the molecules of 

 carbon and hydrogen are oxidized, would be 

 a iiaid and unsatisfactory task. A part of the 

 oxidation, however, takes place in the lungs, 

 where the oxygen molecules are absorbed by 

 the circulating blood from the air, and carried 

 to all parts of the bod^'. Here also carbonic 

 dioxide and aqueous vapor are given off, so 

 that the connecting windpi|)e may be consid- 

 ered as the smoke-stack and exhaust-pipe of 

 the human engine. 



Water is, of course, required both bj' the 

 steam-boiler and the animal. The steam-pipe 

 which carries the force to the cylinder of the 

 engine is best represented in the human body 

 bj' the arteries. The heart is a perfect natural 

 pump ; and a Mveh* imagination might regard 

 the liver as corresponding to the " feed- 

 heater " of the engine, though the comparison 

 would be rather far-fetched. The piston-rods, 

 levers, and other moving parts of the engine 

 are supplied b}' the limbs and muscles ; and if, 

 through excessive action, the "pressure" be- 

 comes too high, we have in the perspiration a 

 safety-valve which at once cools down the 

 lieated system. If the perspiratory ducts be- 

 come clogged, the consequences to the body 

 are almost as serious as the failure of the 

 safety-valve is to the steam-boiler. 



The excretion of the waste products of the 

 body through the natural channels, and the 

 removal of the ashes from under the boiler of 

 the engine, need only to be mentioned to be 

 brought into the comparison. 



Thus we see, that, from a slrictlj' material 



point of view, man is but a piece of machinery, 

 burning carbon, and giving out heat and work. 

 But there the resemblance stops. The engine 

 requires an engineer to run it and keep it in 

 order : but the human engine not onl3- keeps all 

 its complicated machinery working smoothly, 

 but, to a limited extent, possesses the power of 

 repairing its own injuries, and even of repro- 

 ducing other forms like itself; so that, when it 

 is finally worn out, the work of the world will 

 go on. What this mysterious something which 

 we call the vital force is, or whether the en- 

 gineer of the human machine reallj- has his [jost 

 in the brain, as is generally believed, are mys- 

 teries which have hitherto been, and probal)ly 

 always will be, unsolvable. The mechanical 

 and chemical processes of man and machine 

 are closely analogous, but over and above all 

 is the great mystery of life. The giant steam- 

 ship, propelled by its massive and powerful 

 engines, moves across the ocean like some 

 great sea-monster ; but the tiniest speck of 

 organized protoplasm in the depths below, 

 possesses powers which not even the builder of 

 the steamship can bestow, and in comparison 

 with which it becomes but a worthless mass of 

 wood and metal. 



SIMPLE SPHYGMOGRAPHS. - 



The sphygmographs, which show and record 

 the rate and nature of the pulse-beat, are usu- 

 all}- quite complicated and expensive instru- 

 ments. In a recent number of La Nature 

 two forms are illustrated which cost almost 

 nothing, and for many purposes are equally 

 useful with the more expensive ones. 



The first form shows the rate and force of 

 the pulse-beat to the eye, bj- the movemenls 

 of a little flag attached to a wire spring. A 



piece of fine brass wire is soldered at one end 

 to a little metal cup, — a thimble without a 

 top, for example, — and is then bent into a 

 spiral spring, as shown in the engraving, with 

 the straight end passing up through its centre, 

 and provided at the extremity with a little 

 paper flag. On pressing the instrument upon 

 the wrist over the artery, the pulse-beats will 

 be transmitted to the spring ; and the flag will 

 make various movements, according to the 

 condition of the pulse of the person experi- 

 mented upon. If desired, it can easily be 

 arranged so that, at each movement of the 

 upright wire, it shall strike against another 



wire, and close an electric circuit, into which 

 a telephone or electric bell may be introduced, 

 thus rendering the beats perceptible to persons 

 at a distance. 



A still simpler sphygraograph consists of a 

 small piece of looking-glass fastened to the 



wrist bj' a rubber band. A pencil of light, 

 either natural or artificial, is allowed to fall 

 upon the glass, and is reflected upon the ceil- 

 ing, or a screen placed in any convenient posi- 

 tion. By this means the pulsations are greatly 

 magnified, and can be rendered visible to a 

 large number of persons at once. This simple 

 arrangement is especially well adapted for the 

 use of lecturers. 



THE COCA-PLANT. 



Erythhoxylon Coca (Lamarck), of the Lin- 

 nace<e family, is found in the same equatorial 

 countries where cinchona (Peruvian-bark tree) 

 grows It is a small tree, from six to nine feet in 

 height, cultivated in the various parts of South 

 America, principally in Peru and Bolivia, Ecuador, 

 New Granada, and Brazil. Its trunk is covered 

 by a rough, generally glossy bark. Its branches, 

 often compressed near the top, bear alternate 

 leaves, very variable in their dimensions, elliptical, 

 and of a green color, darker on the outside than 

 ou the inside. 



The distinctive character of these leaves is the dis- 

 position of their veins ; viz., there are observed by 

 the side of the middle fibre two longitudinal lines 

 jutting out, which separate at the base of the leaf, 

 and meet again at the point, each describing a 

 slight curve. Its branching root, with oblique 

 divisions, ends in delicate rootlets. Its flowers — 

 small, white or greenish yellow — are found either 

 solitary or grooped in small scaly cavities. Its fruit 

 is a pericarp, containing a seed in which the embryo 

 is usually surrounded by abundant pabulum. 



A light and silicious soil, a mean temperature of 

 from fifteen to eighteen Centigrade, and a certain 

 quantity of moisture, are the essential conditions 

 for the perfect growth of coca. According to 

 Papig, in the valleys of Chiiicao and Cassapit the 

 ground where coca best flourishes is slanting, rela- 

 tively steep, but very fertile, composed of brick-red 

 clay, containing probably some iron. 



Coca-seeds are sown in beds, called " almazigos." 

 The young plants are protected from the heat of 



