August 12, 1909] 



NA TURE 



201 



actions obtainable by stimulation of the abdominal sympa- 

 thetic are not associated with sensation. The distinct 

 reflex contraction of the abdominal muscles resulting from 

 stimulation of the abdominal sympathetic is another re- 

 action which it is difficult to believe is not associated with 

 sensation. The latter phenomenon has a two-fold interest. 

 In the first place, it is the basis of a well-known clinical 

 symptom, the riifid belly wall, and, secondly, it represents 

 a' form of tonic contraction not directly inducible by 

 , artificial stimuli. 



On examining critically Haller's, and to a less extent 

 Lonnandcr's paper, we are struck by the fact that the 

 stimuli used arc unnatural in character. It is not likely 

 that the viscera are equally responsive to all forms of 

 I mechanical stimuli. Twisting, stretching, or squeezing the 

 wall of the intestine from the outside may be ineffective, 

 because the nerve endings in these organs are adjusted 

 for stimuli of another kind. In the case of the bile duct 

 and of the ureters a twist produces no vaso-motor effect, 

 but distension by injection produces a well-marked rise 

 of blood pressure. 



The "referred visceral pain" was discussed next. Dr. 

 J. Mackenzie denies that a viscus is ever directly painful, 

 the pain felt being essentially a "referred one." For 

 example, in pleurisy the lungs and parietal pleura are in- 

 sensitive. While agreeing with Lennander in the view 

 that the subserous layer of the pleura is sensitive, 

 Mackenzie holds that the pain of pleurisy is mainly a re- 

 ferred pain duo to cramp of the muscles of the thoracic 

 wall. Mackenzie gives the following theory as to the 

 mechanism of the different forms of " referred pain." He 

 holds that stimulation of afferent visceral nerves by some 

 influence increases the excitability of afferent centres in the 

 cord connected with corresponding areas of skin. The 

 pain is consequently referred to these cutaneous areas, and 

 is only indirectly the result of stimulation of deep visceral 

 atferents. 



Head gives a somewhat different explanation. Impressed 

 by the fact that inflammation of spinal ganglia produces 

 herpes zoster, he was led to believe that afferent visceral 

 fibres in their passage through the same ganglia as certain 

 afferent cutaneous nerves can affect the adjoining cells 

 connected with the latter and thus produce " referred 

 cutaneous pain." This view is opposed to Miiller's law, 

 and was finally given up by Head. He ultimately trans- 

 ferred the seat of the nervous mechanism from the ganglia 

 to deeper centres in the cord. The segments of the cord 

 connected with " referred pain " do not correspond with 

 the segments of the spinal axis as indicated by the ganglia. 

 Head suggests that the " referred pain " areas correspond 

 with the primitive phylogenetic segments of the cord. He 

 leaves the mechanism of overflow unexplained. .\ remark- 

 able fact is that the area of skin affected by referred pain 

 is a mere patch or couple of patches, not a segment, but 

 nevertheless more or less scgmentally arranged. 



The deep visceral afferents from the heart are not only 

 those which have been most fully investigated experi- 

 mentally, but also form an intermediate group between 

 the pure visceral deep afferents and those of somatic or 

 muscular origin. The chief afferent nerve of the heart is 

 the depressor, and the receptive field for its stimulation 

 is its nerve terminations in the wall of the aorta. The 

 most adequate stimulus is distension of the walls of that 

 vessel. The result of stiinulation is a lowering of blood 

 pressure due to a diminution of vascular tone. The 

 nature of this tone, like that of voluntary muscles, is still 

 obscure. It is doubtful whether stimulation of the de- 

 pressor gives rise to pain directly. The areas of " refejred 

 pain " given by Mackenzie are not cranial, as we should 

 expect, since the vagus is a cranial nerve, but mainly lie 

 in the chest wall. Tender spots, however, are also found 

 on the head. 



Prof. Sherrington then gave a brief survey of deep non- 

 visceral or muscular afferents. Since the work on this 

 subject is largely due to himself, and since he has else- 

 where stated his views more fully, it would not serve any 

 good purpose to try to epitomise this part of his paper. 



The paper was followed by an interesting discussion, in 

 which Prof. J. S. Macdonald, Dr. Graham Brown, and 

 others took part. The discussion chiefly referred to the 

 nature and functions of the terminations of the deep 



NO. 2076, VOL. 81] 



afferent muscular nerves. A number of other papers of 

 anatomical and physiological interest were also read by 

 the following : — Prof. Di.xon (Dublin), the development of 

 the achondroplasic skeleton ; Prof. Anderson (Galway) ; 

 Dr. Dickey (Belfast), the cervical pleura ; Dr. Johnston 

 (Dublin), the intercostal nerves; Drs. Goodall and Earle 

 (London), the structure of the pancreas in relation to its 

 functions; Dr. Maclean (Liverpool), phosphatides in the 

 light of modern research ; Prof. B. Moore (Liverpool), the 

 chemistry of h;emolysis ; Dr. S. Spicer, some points 

 in the inechanics of respiration ; Prof. Thompson, the 

 development of the foetal heart; Dr. Leonard Hill, F.R.S., 

 the influence of inhalations of oxygen on the onset of 

 muscular exhaustion ; Dr. Rutherford, some points in con- 

 nection with the anatomy of the cranium of the fish ; Dr. 

 Waterston, some instruments used in anthropometry. 



W^ 



RECE\T IMPROVEMENTS IN THE INTERXAL- 

 COMBUSTION ENGINE.^ 

 il. 

 E have already explained how important in the 

 economical development of the internal-combustion 

 engine is an accurate and precise knowledge of the physical 

 properties of the working medium. The two chief features 

 ol which a knowledge is required are the calorific value 

 of the explosive mi.xture and the relation between the 

 specific heat and temperature of the ignited gases. The 

 calorific value has been carefully ascertained for most of 

 the gases commonly used, but the specific-heat relation is 

 still a matter of unfortunate uncertainty. At the Leicester 

 meetino- of the British Association in 1907, under the 

 sectional presidencv of Prof. Silvanus P. Thompson, the 

 desirability of clearing up the doubts that surrounded this 

 subject was so keenly felt that an important committee 

 was appointed for " the investigation of gaseous explosions, 

 with special reference to temperature." An account of the 

 findino-s of this committee was published in N.«ure of 

 June ^4 last. From our present point of view the important 

 "result of the committee's work is expressed in the follow- 

 inrt extract from its report :—" Recent researches on the 

 properties of the gases at high temperatures have definitely 

 shown that the assumption of constant specific heat is 

 erroneous and have given sufficient information about the 

 magnitude of the error to show that it is of matenaf 

 importance. . . . The closer approximation to the rea 

 cycle which is made by taking account of the actual 

 properties of the working fluid, though it leads to some 

 complication of formulae, gives compensating advantages 

 of real practical value." This bears out, .also, a remark- 

 made by the late Prof. Zeuner= to the effect that at 

 anv rate there must be dropped from the theory of the 

 internal-combustion motors the former assumption of the 

 constancy of the specific heats of the products of com- 

 bustion." A curve connecting the specific heat at constant 

 volume (Cv) of the mixture of gases, formed by the ex- 

 plosion of one part of coal gas in nine parts of a"", with 

 temperature centigrade (6), which was considered to be 

 accurate within s per cent., was included in the com- 

 mittee's report. A formula which fits this curve closely is 



C„ = o-.72 + o-o75j^*^, 



and although the constant in the second term on the right- 

 hand side of this equation can only be looked upon as a 

 first estimate, however carefully chosen, the equation does, 

 probably, represent the high-water mark in our present-day 

 knowledge, and from it can be deduced the limiting 

 theoretical efficiency of engine cycles in which such a work- 

 ing medium is employed. .. 



It is well known that on the basis of a constant specihc 

 heat the ideal efficiency (tj) can be found from the follow- 

 ing equation, 



where r is the ratio of compression and 7 is the ratio of 

 the specific heats. This relation applies with equal truth 



1 Continued frrmp. 172.''^' 



2 "Technical Thefmodynamics," hy Pro'. Zeuner. 



