76 PULSE RECORDS IN THEIR RELATION TO 



has undergone improvement. Many instruments have been introduced, 

 amongst which those of Hiirthle require special mention. The inertia 

 of the levers and membranes is reduced in Hiirthle's instruments ( 26c ) 

 to an almost negligible quantity. Air is replaced by fluid transmission, 

 for the compressibility of air renders it less reliable in obtaining records 

 free from extraneous movements. The delicacy and reliability of 

 Hiirthle's instruments have been demonstrated by Bayliss and Starling 

 by a photographic method ( 3 ). Hiirthle's differential manometer is so 

 constructed that two columns of fluid, each conveying the changing 

 pressures of a pulsating cavity, are opposed to each other. Any 

 difference in pressure in the two cavities is thus registered, and the 

 instrument is of particular value in ascertaining the instant at which 

 the pressures in two adjoining and communicating cavities, such as 

 auricle and ventricle, or ventricle and aorta, become equal. It is 

 with this instrument that information has been obtained in respect 

 of two " standard movements " of the heart, namely, the opening of 

 the auriculo-ventricular valves and the closure of the semilunar seg- 

 ments. The standard movements, to which further reference will 

 frequently be made, are of importance ; they may be regarded as 

 fixed points of time, and it is convenient to describe and figure all 

 other cardiac movements, and oscillations to which these cardiac 

 movements give rise, in relation to them. The third standard 

 in common use is the commencement of ventricular systole, or 

 perhaps more accurately, the moment at which the pressure in the 

 ventricle commences to rise in systole. The onset of systole is an 

 instant which it is not difficult to fix in animal experiments ; but 

 in man, as will subsequently be seen, it is by no means so easy. It 

 is possible that with the further elaboration of Einthoven's recently 

 introduced electrical method l more accurate indications may be 

 obtained. Einthoven uses a sensitive " string galvanometer " to 

 estimate the change of potential in the limbs, which occurs with 

 the heart beat. The observations, however, which have as yet been 

 made, have little bearing upon the subjects of this article. 



In conclusion, the attempts instituted to obtain graphic records 

 of the heart sounds may be briefly referred to. Einthoven 

 and Geluk ( e ) employed a microphone and capillary electrometer. 

 Hiirthle ( 26b ) also used the microphone for a similar purpose. Obser- 

 vations which are referred to in the text have thus been carried out 

 on the instants of onset of the first and second sound ; but given more 



1 Archives Internal, de Physiologie, vol. iv., 1906-7, pp. 132-164; Archir. 

 f. d. ges. Physiol., Bd. 122, 1908, s. 517-584. 



