PHYSIOLOGY. 



663 



of about one half an atmosphere, and found thai, 

 at each systole of the heart the volume of blood 

 ejected exactly equals that which the same ani- 

 mal shows under normal pressure Thus, if the 

 tension of the oxygen breathed is reduced one 

 half, the effect on the circulation is as slight as it 

 is on the respiration. With still greater rare- 

 faction the oxygen tension in the alveoli can, by 

 deeper respiration, still be brought to the level 

 where the haemoglobin of the blood is saturated, 

 and no distress appears. Dr. Loewy drew in- 

 teresting conclusions from his experiments in 

 relation to the meaning of mountain sickness. 



Among the results recorded by Leonard Hill 

 of his research upon the influence of the force 

 of gravity on the circulation were the following : 

 That this force must be regarded as a cardinal 

 factor in dealing with the circulation of the 

 blood; that the important duty of compensating 

 for the simple hydrostatic effects of gravity in 

 changes of position must be ascribed to the 

 splanchnic vasomotor mechanism; that the effects 

 of changing the position afforded a most delicate 

 test of the condition of the vasomotor mechan- 

 ism ; and that the amount of compensation de- 

 pended largely on individual differences. The 

 compensation is far more complete in upright ani- 

 mals such as the monkey than in rabbits, cats, 

 or dogs, and therefore is probably much more 

 complete in man. When the power of compen- 

 sation is damaged by paralysis of the splanchnic 

 vasoconstrictors, induced by severe operative 

 procedures or by injuries to the spinal cord, by 

 asphyxia, or by some poison, such as chloro- 

 form or curare, then the influence of gravity be- 

 comes of vital importance. The feet-down posi- 

 tion is of far greater moment than the feet-up 

 position, because when the power of compensa- 

 tion is destroyed the blood drains into the ab- 

 dominal veins, the heart is emptied, and the 

 cerebral circulation ceases. Generally the feet- 

 up position occasions no ill consequence. If 

 the heart is affected,, as by chloroform or curare 

 poisoning, the restoration of pressure is incom- 

 plete, and it is possible that the heart may be 

 stopped altogether by the inrush of a large 

 quantity of blood, caused by too rapid an appli- 

 cation of pressure on the abdomen. Chloroform 

 rapidly paralyzes the compensatory vasomotor 

 mechanism and damages the heart. Ether, on 

 the other hand, only paralyzes the compensatory 

 vasomotor mechanism very slowly. The vaso- 

 motor paralysis induced by these anaesthetics 

 lasts for some considerable time after the re- 

 moval of the anaesthetics. Compression or ele- 

 vation of the abdomen, coupled with artificial 

 respiration and with squeezing of the heart 

 through the thoracic walls, is the best means of 

 restoring an animal from the condition of chlo- 

 roform collapse. 



The main results of experiments by T. Lander 

 Brunton and F. W. Tunnicliffe on the effect of 

 massage on the circulation are, that during the 

 massage of muscles the flow of blood through 

 them is increased; that immediately after the 

 cessation of massage an accumulation of blood 

 occurs in the massaged muscles, and this is rap- 

 idly followed by an increased flow through the 

 muscles ; and that the massage of a considerable 

 muscular area causes at first a slight rise in the 

 general blood pressure, which is followed by a 



fall that in some cases amounts to one fifth of 

 the initial blood pressure. 



It was shown by Mr. Bayliss that the fall of 

 blood pressure which follows the excitation of 

 the central end of the depressor nerve -is accom- 

 panied by vasodilatation, of which evidence is 

 afforded in the case of the kidney by the simul- 

 taneous expansion of that organ, and in the case 

 of the lower limbs by their increase in volume. 

 As the vasoconstrictors leave the spinal cord by 

 the lower lumbar roots the section of the cord in 

 the dorso-lumbar region will cut off the vaso- 

 constrictors; and since, under these circum- 

 stances, the stimulation of the depressor still 

 causes an increase in the volume of the limb, 

 the author was led to conclude (a) that the dila- 

 tation was really due to the increased activity 

 of vasodilator centers, arid not to the dimin- 

 ished activity of vasoconstrictor centers; and 

 (b) that the anterior roots by which the vaso- 

 dilator nerves of the lower limbs leave the cord 

 extend higher into the dorsal region than is 

 the case with constrictor nerves. Corroborative 

 experiments were carried out in which the cord 

 was left intact, while the sympathetic, in which 

 the vasodilators run, was divided. Under these 

 circumstances no increase in the volume of the 

 limb accompanied the depressor excitation be- 

 cause the dilator supply was cut off. 



Experiments by Prof. Hill show that under 

 normal conditions the intracranial pressure 

 hardly ever exceeds 10 millimetres of mercury. 

 The author finds, further, that 20 cubic centi- 

 metres of the fluid can be slowly driven into the 

 subdiiral space at the rate of 1 cubic centimetre 

 per minute without harm ; but that if a larger 

 quantity be injected an immense rise of arterial 

 pressure takes place, with acceleration of the 

 heart's action and inspiratory gasps at long in- 

 tervals, which are followed by fall of arterial 

 pressure and death. 



Prof. Schafer exhibited photographs in the 

 British Association to illustrate a research made 

 by Dr. Oliver and himself as to the functions of 

 the suprarenal bodies. They were chiefly photo- 

 graphs of tracings indicating the blood pressure, 

 the heart beats, and the volume of the blood 

 vessels in such localized parts as a limb or the 

 kidney. The injection of suprarenal extract 

 was seen to cause a great rise of blood pressure, 

 due not to any modification in the heart beat 

 but to the constriction of the blood vessels, this 

 constriction being dependent upon the integrity 

 of the central nervous system. 



An account is given by Dr. Starling of ex- 

 periments which have led him to believe that 

 the flow of lymph from the thoracic duct is de- 

 pendent upon the amount of blood pressure in 

 the liver capillaries, and hence that the old me- 

 chanical theory of lymph formation is correct 

 as regards this source of lymph flow. He finds 

 that obstruction of the inferior vena cava must 

 raise the pressure in the portal capillaries, and 

 that a similar result follows obstruction of the 

 abdominal aorta. The flow of lymph which 

 Heidenhain observed after these operations was 

 not therefore necessarily due to secretory activity, 

 but must occur in consequence of the pressure 

 even if the permeability of the portal capillary 

 walls remains unaltered. Similarly the injection 

 of a large quantity of saline into the circulation 



