Feb. 26, 1874] 



NATURE 



327 



THE HEART AND THE SPHYGMOGRAPH* 

 T N the same way that by the spectroscope much can be 

 •^ learned as to the chemical constitution and the phy- 

 sical changes going on in the sun, so by the sphygmo- 

 graph applied to the artery at the wrist many of the most 

 important phenomena occurring in the heart can be 

 studied with a facility that cannot bs otherwise attained. 

 Till the introduction of the sphygmograph of Marey the 

 pulse was considered to be little more than a simple up 

 and down movement, because the instruments employed 

 to register it, such as those of Herisson, Ludwig, and 

 Vierordt, developed so much momentum that the details 

 of the true trace were disguised. In the instrument as at 

 present employed, the substitution of counterbalancing 

 springs instead of weights has so far improved its effi- 

 ciency, that the pulse is now known to form a decidedly 

 complicated curve if its movements are allowed to record 

 themselves on a moving paper. The sphygmograph 

 trace, as thus produced, gives indications in two direc- 



tions ; first, as to the action of the valves of the heart ; 

 and secondly, as to the manner in which the muscular 

 walls of the ventricles perfornt their work. It is to the 

 former of these subjects that most physiologists have 

 directed their observations in employing the instrument ; 

 bat it is to the latter, the more important of the two, that 

 it is my intention to direct attention on the present occa- 

 sion. 



The heart being nothing more than a pump of a pecu- 

 liar construction, much may be learned by contparing it 

 with other artificially constructed machines for the same 

 purpose. In most such machines the force which keeps 

 the pump at work is constant in power, in other words it 

 does not vary automatically in efficiency with the amount 

 of work that is expected of it. In the locomotive engine, 

 however, there is an arrangement by which the furnace 

 becomes hotter as the speed at which it moves is in- 

 creased, the waste steam pipe opening into the funnel and 

 so varying the amount of the draught through the bDiler 

 tubjs. With this arrangement it is nevertheless evident 



.'V-itomiitic.iIly Working-engine, when supplied with coal-j 



that there is a great waste of fuel in the construction of 

 the furnace. 



It is quite possible to construct a steam-engine on 

 much more economical principles, and the accompanying 

 figure illustrates the manner in which the small engine on 

 the table is at present working (sec Figure). The boiler {a) 

 being sufficiently heated, drives the engine {b), which per- 

 forms work by pumping conl-gas from the tube c through 

 the pump (/, into the elastic reser\-oir e. From this elastic 

 bag most of the coal-gas escapes, through the tube/, into 

 an ordinary gas bag, but a tube {g) carries some of it to 

 supply the Bunsen's burner (//) which heats the boiler. It is 

 evident that with this arr.angement the size of the flame of 

 the Bunsen's burner (//), and therefore the pressure of steam 

 in the boiler, which is the same as saying the efficiency 

 of the engine, varies with the amount of work required of 



• Abstr.icl of .-i lecture deli%'er(;d by Mr. A. H. Garrod at the Royal Insti- 

 tution on the evening of Friday, Feb. t). 



that engine ; for the greater the pressure in the elastic 

 bag, the harder is it for the engine to perform the work re- 

 quired of it, and the greater is the burner-flame. With a 

 certain proportion between the sizes of the orifices of the 

 taps and the extensibility of the elastic bag and tubes, it 

 would be possible to arrange this engine in such a manner 

 that, within certain limits, the velocity of the fly-wheel 

 would not vary with the pressure in the elastic bag ; in other 

 words, with the work to be done. That the heart is a 

 pump constructed on thj same principle as this engine is 

 the teaching of the sphygmograph, as far as it is in my 

 power to interpret its curves, the proof resting on the fol- 

 lowing considerations. 



First, the analogy between the anatomical distribution 

 of the arteries and the different parts in connection with 

 the engine is not difficult to trace. Tne coal-gas corre- 

 sponds to the blood, the boiler {a) together with the engine 

 ip) to the muscular tissueofthe heart, whose left ventricular 



