Sept. 5, 1872] 



NATURE 



373 



they may be. This single reading of the total amount of cicep 

 being divided by tlie number of times the experiment was re- 

 peated, and by the given number of degrees of heat through 

 wh'ch it had been each time succ»ssively raised, and by the original 

 length of the bar, will give the desired coefficient of expansion. 



I think that results obtained by this mode of translation will, 

 for minute expansions, be more reliable than those obtained 

 either by Lavoisier and Laplace's method, or by that of Rry and 

 Ramsden. Thomas Stevenson 



Baden-Baden, August 26 



Origin of Insects 



In Nature of December 7, 1S71, there is an interesting 

 letter from Mr. B. T. Lowne, on the Origin of Insects, in which 

 the writer refers to Fritz MiiUer's " Facts for Darwin" in favour 

 of the opinion that " the larval forms of insects are probably 

 derived from imaginal " or perfect forms. I have not at present 

 any opinion to offer on this subject ; but, though I estimate 

 very highly indeed the light which Fritz Miiller has thrown on 

 the Crustacea, I think nothing can be more unsatisfactory than 

 his remarks on insects. He concludes that the earliest insects 

 resembled the wingless Blattidre, overlooking, what is obvious 

 enough, that any theory of the origin of insects ought to ac- 

 count for, or at least show the origin of, those most charac- 

 teristic organs of the class, the wings. I quite agree with Mr. 

 Lowne that " it is extremely probable that insects first emerged 

 from the water w'ith fully-formed wings." I think it scarcely 

 possible to doubt that the wings were originally organs of aquatic 

 respiration. But this does not answer the question of the origin 

 of insect metamorphoses, which, though an evolutionist, I think 

 one of the greatest difficulties of the theory of evolution ; it 

 does not answer the question whether the perfect forms with 

 ■wings and legs have been derived from the larval forms without 

 either, or the converse. 



Mr. Lowne goes on to say, "We have still relics of an aquatic 

 winged insect fauna in the hymenopterous genus, discovered by 

 Sir John Lubbock." I cannot think this brings us any nearer to 

 the origin of insects. It could not do so unless the Hymenop- 

 tera were at or near the origin of the class, and this will scarcely 

 be maintained. The Hymenoptera are probably the higlitst of 

 all insects — certainly so if instinct is the criterion. The aquatic 

 Ilymenopteron (1 do not know its name) is no more a relic of 

 the origin of insects than are the water-beetles ; and no one will 

 say that the Coleoptera are near the origin of the class. It is 

 true that the water-beetles are wingles?, while the Hymenopteron 

 in question is winged ; but the beetles are a winged order, and 

 those which have no wings have lost them. Indeed, it is only 

 in a functional sense that any beetle is wingles.=, for they all 

 retain the wing-covers, which are modified wings. It is probably 

 true that the origin of all animals whatever was aquatic, but it 

 does not follow that the aquatic members of any class denote 

 the origin of the class. The aquatic habits and stnicture may be 

 only adaptive. No one would look to the seal or the hippo- 

 potamus for the origin of the Mammalia. 



Joseph John Murphv 



THE LAW WHICH PECULATES THE 

 FREQUENCY OF THE PULSE 



FROM a pamphlet on this subject, recently published 

 by Mr. A. H. Garrod, we extract the following 

 summary of the main features of the circulation : — 



" The circulation of the blood is maintained by the 

 repeated contraction of the heait. Each cardiac revolu- 

 tion is divided irito three parts— the s) stole, the diaspasis, 

 and the diastole. The following laws hold with regard to 

 the length of these intervals : — 



" I. The systole, together with the diaspasis— or, in 

 other words, the first cardiac interval — varies as the 

 square root of the whole revolution. 



" II. The systole varies as the square root of the 

 diastole. 



" III. The diaspasis is constant. 



"The amount of work that the hcait has to perform 

 in maintaining the circulation depends on two sets of 

 changes which may occur in the systein : i. Variations 

 in the blood pressure ; 2. Variations in the resistance 

 to the outflow of that fluid from the arteries. 



" As the capacity of the arteries, including the ventricles, 

 varies directly as the blood pressure, and as the flow of 

 blood from the capillaries does the same, the frequency of 

 the heart's beats is dependent on the resistance to the 

 capillary outflow, and not at all on the blood pressure ; in 

 other words, the heart always recommences to beat when 

 the blood pressure in the systematic arteries has fallen a 

 certain invariable proportion. 



" Variations in blood pressure result from : I. Absorp- 

 tion into, and excretion from, the vascular system of 

 fluids ; 2. Changes in the capacity of the arterial system, 

 which occur on the contraction or relaxation of the mus- 

 cular arteries ; 3. Changes in the amount of available 

 blood, which result from the ha;mastatic dilitation of some 

 of the yielding vessels on altering the position of the body. 

 As changes in the first of these cannot be very suddtn, 

 and those in the latter are never very considerable, the 

 mean blood pressure in health varies but little during 

 short intervals. 



" Variations in peripheral resistance result from : 

 I. Different degrees of tonicity or patency of the mus- 

 cular arteries ; 2. Different resistances in the venous 

 systein. The former may occur independently in one or 

 other system of vessels, as the cutaneous or the alimen- 

 tary ; also mechanically from pressure on a part of the 

 body. The latter are insignificant in health. 



" The heart depends for its power of doing work on 

 chemical properties in the blood it pumps into the sys- 

 temic vessels, and as the blood reaches it direct from 

 those vessels, the cardiac intramural circulation varies 

 with the changes in the former ; and the length of the 

 systole varying only as the square root of the time of 

 diastole, the degree of cardiac nutrition varies directly as 

 the systematic blood pressure, and as the square root of 

 the diastolic time. The coronary arteries supplying the 

 whole heart, the work done by the right ventricle is 

 governed by that done in the left ; thus the supply of 

 blood in the left auricle is always rendered sufficient for 

 the requirements of the systemic circulation ; though, as 

 there is no reason for beheving that the resistance in the 

 pulmonary vessels varies with that of the systemic, there 

 must be soine peculiarities in the former circulation 

 (which may explain the variations in the ratio of the 

 number of pulse beats to respirations in some cases). 



" The auricular contraction is a very small force, and 

 its function is most probably to close the tricuspid and 

 mitral valve. 



" The heart commencing its systole as a whole, it is 

 highly probable that the impulse for action is given by a 

 force which affects both ventricles ; such is found in the 

 coronary circulation and the active diastole produced by 

 means of it." 



THE CONGRESS OF PREHISTORIC 

 ARCHyEOLOG V 

 'T^HE meeting of the International Congress of Archa:- 

 -'- ology at Brussels was brought to a close last Friday, 

 August 30. On the previous Tuesday General Faidherbe 

 spoke en the Dolmens, of which he had made a special 

 study in Algeria. He believes them to be the work of 

 soine people whose traces can be found from Pomerania 

 to the coast of Africa, and of whose migrations they in- 

 dicate the halts. Mr. Franks, of the British Museum, 

 piesided on the afternoon of the same day, when the dis- 

 cussion turned chiefly on the primitive races of Belgium. 

 On Wednesday the last expedition of the Congress took 

 place, Namur and the Camp of Hastedon, distant about 

 two kilometres from Namur, being the places selected. 

 The establishment of this camp, covering an area of from 

 eleven to twelve hectares, is attributed to the men of the 

 Polished-Stone peiiod. It is situated on a high plateau, 

 and the cuttings made through the ancient enclosure viere 

 explained by M.Dupont, Director of the Brussels Museum. 



