PHYSIOLOGY. 



691 



This conclusion has been reviewed by Messrs. 

 Langley and Eves, of Cambridge, who suggest 

 that no mention is made in the account of the- 

 experiments of the ^aliva having been neu- 

 tralized before the addition of the acid ; hence 

 the office of the acid may have been simply to 

 render an alkaline saliva neutral a condition 

 which is found to make the action of the fer- 

 ment stronger. Their own experiments show 

 that the action of neutralized saliva is dimin- 

 ished by the presence of .005 per cent of hydro- 

 chloric acid. Regarding it as an open question 

 whether ptyalin acts best in a neutral, a faintly 

 acid, or a faintly alkaline medium, but certain 

 that a distinctly acid or a distinctly alkaline 

 medium retards its action, they suggest that 

 the cases in which the addition of minute quan- 

 tities of acid have appeared to have had the 

 stimulating effect observed may be accounted 

 for by supposing that the acid combined with 

 the proteids present, rather than that any free 

 acid actually existed in the fluid. From further 

 experiments in the action of various agents on 

 ptyalin, they find that when saliva is neutral- 

 ized and then diluted, to prevent any consider- 

 able part of the acid being taken up by the 

 proteids, .005 per cent of hydrochloric acid pro- 

 duces a very destructive effect; that sodium 

 carbonate has a very slight destructive but a 

 powerful retarding action ; and that neutralized 

 saliva converts starch into sugar more quickly 

 in the presence of neutral peptone than in the 

 presence of acid, .002 per cent and upward. 



THE CIRCULATION IN THE BRAIN. Signor 

 Mosso, who for several years past has been en- 

 gaged on the study of the circulation in the 

 brain, has lately published an account of his ob- 

 servations which have yielded some very inter- 

 esting results. He had the rare good fortune 

 to meet with three patients who had holes in 

 their skulls, and was thus enabled to examine 

 the encephalic movements dependent on the 

 changes in the circulation within the organ. 

 No part of the body exhibits a pulsation as 

 varied in form as that in the brain. Signor 

 Mosso describes it as tricuspid ; that is, it con- 

 sists of a strong beat preceded and followed 

 by lesser beats. It gathers strength when the 

 brain is at work corresponding with the more 

 rapid flow of blood to the organ. The increase 

 in the volume of the brain does not depend 

 upon any change in the respiratory rhythm ; 

 for, if we take the pulse of the forearm simul- 

 taneously with that of the brain, we cannot 

 perceive that the cerebral labor exerts any in- 

 fluence on the forearm, although the pulsation 

 in the brain may be considerably modified. 

 The emotions have a similar effect upon the 

 circulation of the brain to that of cerebral labor. 

 Mosso also observed and registered graphically 

 the variations of the cerebral pulse during 

 sleep. Generally the pulses of the wrist and 

 of the brain vary oppositely. At the moment 

 of waking, the pulse at the wrist diminishes, 

 while that of the brain increases. The cerebral 

 pulsations diminish as the sleep grows deeper, 



and at last become very weak. Outward ex- 

 citations determine the same modifications dur- 

 ing sleep as in the waking state, without wak- 

 ing the sleeper. A deep inspiration always 

 produces a diminution in the volume of the 

 brain, in consequence probably of an increased 

 flow of blood into the veins of the thoracic 

 cavity ; the increase in volume of the brain, 

 when it takes place, is, on the contrary, due 

 to a more abundant flow into it of arterial 

 blood. 



INFLUENCE OF THE BLOOD-CONSTITUENTS ON 

 THE CONTRACTION OF THE VENTRICLE. Dr. 

 Sidney Ringer, of University College, London, 

 has described a series of experiments made to 

 ascertain the influence which each constituent 

 of the blood exercises on the contraction of the 

 ventricle. He employed, as his principal fluids, 

 a "saline solution," or the ordinary .75 per 

 cent solution of sodium chloride, and " blood 

 mixture," made from dried bullock's blood dis- 

 solved in water to represent normal blood, and 

 diluted with five parts of saline solution. When 

 the circulating fluid consists only of " saline so- 

 lution," the ventricular beats undergo a series 

 of remarkable changes. The contraction at 

 first becomes more complete if the ventricle 

 empties itself imperfectly. The trace repre- 

 senting the beatings soon becomes broader 

 and its summit rounder, while there is a slight 

 diastolic contraction (persistent spasm). Next, 

 the period of relaxation becomes greatly pro- 

 longed, and the whole trace is permanently 

 raised higher above the base line. During 

 these changes affecting the expansion of the 

 ventricle the contraction is very little altered, 

 or is rather accelerated. Next, the prolonga- 

 tion of the ventricular dilatation grows less, 

 while the trace rises still higher above the base 

 line. In a series of contractions excited after 

 a stand-still of some fifty or sixty seconds, the 

 first contraction dilates more rapidly than the 

 subsequent ones. The changes in the trace in- 

 crease, the amplitude and duration of each 

 contraction grow less, and the dilatation often 

 becomes less prolonged. At the same time the 

 ventricle undergoes another curious change. 

 After the contractions have become weakened, 

 the duration of the contraction and the slow- 

 ness of dilatation are influenced by the strength 

 and duration of the stimulus. Also, if the 

 faradaic excitations be continued till the trace 

 has nearly completed its rise, the contraction 

 is much prolonged. The effect of an increase 

 in the strength or duration and number of 

 stimuli does not occur in a heart fed with 

 blood, nor, in the early stages, with saline. 

 When the dilatation is greatly prolonged, in 

 many cases it is completed at the base while 

 the rest of the ventricle remains quite con- 

 tracted, and then it extends gradually to the 

 apex. Sometimes, before the dilatation has 

 spread far down the ventricle, the dilated por- 

 tion contracts again, and there ensues a partial 

 fusion of the excursions in the trace; in fact, 

 we get an imperfect tetanus, the fusion being 



