iS THE MECHANISM OF THE CIRCULATION. 



and that the pressure height can be read off directly on a dial, while the 

 pressure curve is simultaneously recorded. 1 



For the determination of the relations of the pressure changes in any 

 two cavities, Hiirthle has constructed a differential spring manometer. In 

 this instrument two cannulse are brought into connection with tambours 

 placed on either side of the fulcrum of a lever. This lever works against a 

 spring, which sets in motion a writing-style. When the pressures are equal, 

 the style will remain at rest, and will rise or descend according as the pressure 

 in the one rises above or falls below that of the other. 2 



The curve of intraventricular pressure. — The tracings of 

 Chauveau and Marey, Tick, Hiirthle, Fredericq, all exhibit a curve 

 which is marked by a very steep ascent, followed by a maintained 

 plateau which either rises or falls slightly, or remains horizontal. On 

 this plateau occur two or three small waves ; thence follows the steep 

 line of descent. 3 



The curves obtained by v. Frey and Krehl, Kolleston, Eoy and 

 Adami are of a different type : these show either no plateau, or 

 else a kind of rounded plateau which subsides quickly into the 

 descent. 



The differences in the curves depend almost entirely on the 

 instruments employed, because all the researches have been carried out 

 on clogs, except those of Chauveau and Marey on the horse. The best 

 instrument, as we have seen, is that with the shortest delay, so long as 

 the inertia of the instrument is not too great. 



Contejean has passed a hollow needle into the right ventricle, and 

 allowed the blood to spirt on to a revolving drum covered with white 

 paper ; in this way he has obtained a htemautograph of the intra- 

 ventricular pressure. A plateau is found on such a tracing. 4 



Lastly, Bayliss and Starling have demonstrated the accuracy of the 

 plateau curves by a new method. They connected the intracardiac 

 cannula with a capillary glass tube, which had been partially filled with 

 MgS0 4 solution, and had then been sealed at the top. They photographed 

 on a moving sensitized plate the movements of the meniscus of the 

 fluid in the capillary tube. At the same time the movements of a style 

 affixed to a vibrating tuning-fork were also photographed. 



Within the rates of pressure variations which occur in the heart, 

 the inertia of the fluid was found to be nil, while the volume of 

 fluid moved for a rise of 100 mm. Hg pressure was only -0335 

 c.mm. In Hiirthle's smallest manometer, this volume for the same 

 rise of pressure was 100 c.mm. 5 This method is therefore by far 

 the most perfect yet invented for arriving at the true curve and 

 time relations of intracardiac pressure. Unfortunately, it is too 

 inconvenient to employ habitually. By its means, however, we are 

 assured that the Hiirthle manometer and the sphygmoscope are instru- 

 ments of precision. 6 



The curves obtained by Bayliss and Starling are no doubt a true 

 representation of the intraventricular pressure changes, and it is 



1 Centralbl.f. Physiol., Leipzig u. Wien, 1896, Bd. x. S. 330. 



2 Hiirthle, Arch. f. d. ges. Physiol., Bonn, 1891, Bd. xlix.'S. 45. 



:| Chauveau and Marey, M&m. Acad, de vied., Paris, 1863, tome xxvi. p. 298. 

 4 Arch, dc physiol. norm, ct path., Paris, 1894, p. 821. 

 r °Arch.f. d. ges. Physiol., Bonn, 1888, Bd. xliii. S. 409. 



6 Bayliss and Starling, Internat. Monatschr. f. Anat. u. Physiol., Leipzig, 1894, 

 Bd. xi. S. 426. 



