446 



NATURE 



{Sept. 26, 1872 



by which these rays are carried outside of the object-glass of the 

 telescope or the eye of the observer. Tliese rtevia'.iuns are pro- 

 duced by extraordinary refractious or irregularities in layers of 

 air condensed or r.irificd, placed at i^reat distance from the 

 observer, and at the precise spot where by atmospheric disper- 

 sion the rays of the ditTerent colours directed by the object-glass 

 are separated from one another, so as to be only partly contain d 

 in the irregularly refracting layers o( air. The most important 

 result of M. Respighi's observations is this : — the layers of hetero- 

 geneous air are not reached by the luminous rays of different 

 colours liy means of the internal movement of atmosphtric 

 masses, but by their general movement caused by the rotation 

 of the earth ; which showi tliat the rotation of the earth is one 

 of the principal elements in causing the twinkling of the stars. 

 M. Respighi next described a very ingenious zenith telescope by 

 means of which he can obtain the zenith distance of stars in 

 their passage across the meridian. 



In the Section of Geography, PuliticalEconomy and Statistics, 

 various papers were read on methods of education. 



The first session of the Association lasted eight full 

 days, during which excursions were made to Arcachon, and 

 to the Troglodyte Caves of Eyzies. On the condition and 

 civilisation of the people whose remains .they contain, 

 M. Broca gave a very interesting lecture, in which he 

 co.icluded that these men were savages, but in a state of 

 partial civilisation, having at their disposal abundant 

 food, and consequently leisure, applying themselves to 

 the arts, and already exhibiting the pertectibility of the 

 race. Another excursion was made to the Pointe de 

 Grave, and one, wh ch lasted three days, to the Industrial 

 and Scientific establishment of Landes as far as Bidassoa. 

 The Monday, Wednesday, Thursday, and Friday were 

 devoted to si-anccs, the morning for the sections, and the 

 afternoons for general meetings. These public meetings 

 were well attended, especially the evening lectures of 

 MM. Broca and Corn u, who had audiences numbering 

 about 800. Much intertst was also manifested in the 

 narratives of MM. Janssen and Respighi, who recounted 

 the results of their researches into the constitution of the 

 sun, and of their visit to India last year. 



The reports of the Congress speak in lavish terms of 

 the hospitality and considerateness in all respects of the 

 Bordelais, whose city seems to be one of the foremost in 

 France in respect of educational and scientific institutions. 

 There can be no doubt about the success on the whole of 

 the first meeting of the French Association ; and we only 

 hope that by the time it re-assembles at Lyons next year 

 it will have advanced to the same ratio as it has done from 

 its foundation till now, and that ere very long it will have 

 taken as firm root as a recognised and universally bene- 

 ficial French institution, as the British Association has 

 done among ourselves. 



ON PULSE FREQUENCY AND THE FORCES 

 WHICH VARY IT* 



T^HE cii'culatiun of the blood is an uniform circulation, the 

 pulsations being neglected, and a uniform circulation is one in 

 which the quantity of fluid flowing through all segments of the 

 circulating system is the same ; otherwise there would be a ten- 

 dency for the fluid to accumulate at certain points, which is 

 contrary to the premises. 



To arrive at precise conclusions respecting the circulation 

 there are two points which must be considered — 1st., The laws 

 which regulate the flow of fluids through capillary tubes. 2nd., 

 The variations in the capacity of the circulating system under 

 different pressures. These will be considered separately. Poi- 

 seuille found that the flow of fluids through capillary tubes 

 varies directly as the pressure and as the fourth power of the 

 diameter of the tubes. The author has verified the former of 

 these results on the vessels of the animal system by a different 

 method. Respecting the capacity of the arteries and ventricles 



* Paper read before the British Association at Brighton in Section D, 

 Department of Anatomy and Physiology,) by A. H. Garrod, 



under ditTerent blood pressures, it is evident that the capacity 

 of the firmer must depend on the pressure only, for they are 

 simple elastic tubes, and must be more capacious under high 

 than under low pressures ; reasons are given below for a more 

 precise statement of this relation. To maintain a uniform cir- 

 culation with a pulsating motor, like the heart, it is evident from 

 the above considerations that variations in the resistance at the 

 small areries must produce variations in pulse-rate ; and that 

 unless the capacity of the arteries and heart vary directly as the 

 pressure, variations in blood pressure must be also attended with 

 change in pulse frequency. That the cap.icity of the ventricles 

 is dependent on the arterial blood pressure can be proved by tlie 

 varied amount of opening up of the ventricular cavities which 

 follows different fluid pressures in the coronary arteries. 



Next, the different forces which vary the pulse-rate must be 

 considered. It can be shown that any change in the resistance 

 to the flow of blood through the capillaries varies the pulse-rate, 

 increased resistance rendering the pulse slower and the reverse. 

 As instances of these effects may be given, the pulse-siowing 

 effects of stripping in a cold air, of a cold bath, and of compies- 

 sion of large arteries ; the pulse-quickening eflfects of a hot bath, 

 whether air or water. Numerous experiments by the author 

 prove that the effect of copious blood-letting is not to modify 

 the pulse-rate at all, thus showing that the law given by Marey 

 respecting pulse frequency is not correctly based. The above 

 points, namely the law of Poiseuille, the dependence of the ca- 

 pacity of the arteries and ventricles on the pressure of the blood, 

 the dependence of the pulse-ra e on the peripheral reoislante and 

 its non-dependence on the blood pressure, can all be correlated 

 by only one theory, namely, that the heart always re-commences 

 to beat when the tension or pressure in the arteries has fallen 

 at invariable proportions, which also assumes that the capacity 

 of the heart and arteries varies directly as the pressure. The 

 facts that the arteries are generally empty after death, and that 

 the cavity of the heart is sometimes found to be obliterated on 

 >-!gor mortis, show that absence of pressure and capacity go 

 together. 



This theory explains the known peculiarities in pulse rate 

 attending change in position, by showing that while standing 

 all the pressure of the body weight is borne by non-compressible 

 rigid tissues and so the circulation is normal, but while lying, 

 the soft parts are compressed and resistance introduced into 

 the circulation, reducing the rapidity of tension-fall, and 

 therefore the frequency of the pulse ; an intermediate condition 

 a tends the sitting posture. The pulse quickens during inspi- 

 ration, and becomes slower during expiration ; for during the 

 former act the reducing pressure in the chest lowers the aortic 

 blood pressure, and makes the tension-fall more rapid, while 

 in expiration the reverse occurs. 



This theory also is the only one which throws light on the 

 cardiograph law published by the author (see 'Journal of 

 Aimtoiiiy aiiii Pliysiology, 1870-73), which may be thus stated 

 — For any given pulse-rate the first part of the heart's revo- 

 lution has a constant length, but it varies as the square root of 

 the length of the complete pulsation. The pulse-rate not 

 depending on the blood pressure, and the length of the first 

 cardiac interval not varying when the rate is constant, its 

 length also does not depend on the blood pressure. The first 

 cardiac interval may be divided into the systole and the 

 interval between that and t' e closure of the aortic valve (the 

 diaspasis) ; these combined not varying as the blood pres- 

 sure, it is almost certain that separately they do not do so 

 either ; so it may be said that neither the length of the 

 systole nor of the diaspasis tlepends on the blood pressure. 

 But the fall of tension between the pulse beats being but 

 small, and the diaspasis lengih not depending on the blood 

 pressure, there is no reason why it should vary in length with 

 difl^erent pulse-rates ; and assuming this in connection with the 

 measured diaspasis length in a particular case ('00183 of a 

 minute), it can be deducted from the above cardiograph law, 

 that the systolic length varies as the square root of the diastolic. 

 From these facts the relation of the nutrition of the heart to the 

 time of heart nutrition (diastole); and to the blood pressure, m.ay 

 be deduced ; for the systolic length not varying with the blood 

 pressure when the pulse rate is constant it is evident that the 

 cardiac nutrition must vary directly as the blood pressure in the 

 aorta ; and the systole varying as the square root of the diastolic 

 time, shews that the nutrition of the heart varies as the square 

 of the time of nutrition (diasttile), for with a quadruple resis- 

 tance to the peripheral circulation, the heart would be four times 



