748 



PHYSIOLOGY, RECENT. 



PHYSIOLOGY, RECENT. Physiological sci- 

 ence has made great advances under the sys- 

 tem of specialized minute investigation of the 

 different tissues and organs of the body and 

 their functions which is now very generally 

 applied. Nearly every vessel and nearly every 

 tiuid of the body has been subjected under this 

 system to a most rigid and searching micro- 

 scopic, chemical, and dynamic examination, 

 and is thereby being made to disclose the most 

 intimate secrets of its structure and function. 

 Dr. Ferrier and Professor Yeo have added to 

 the clearness of the evidence of the localization 

 of function in the cortex of the brain from ob- 

 servations made in their experiments on monk- 

 eys. They are able, after having effected a lo- 

 calized or limited lesion by means of the gal- 

 vanic cautery of the surface of the brain, to 

 predict the precise phenomena of paralysis 

 which will occur. On microscopical examina- 

 tion after death following these phenomena, 

 strands of fibers proceeding from the damaged 

 parts of the cortex may he traced down to the 

 motor or sensory ganglia at the base of the 

 brain, and thence downward through the spi- 

 nal cord to the muscles paralyzed by the lesion. 

 Exner, who has been engaged in considering 

 localization in the function of the brain by the 

 aid of the phenomena presented by patholog- 

 ical changes, has satisfied himself by that meth- 

 od of the existence of very limited areas on the 

 surface of the brain, destined to receive im- 

 pressions and original motor impulses. Cou- 

 ty's researches on the same point, published 

 in Brown-Sequard's " Archives," appear to be 

 altogether opposed to Ferrier and Hitzig's con- 

 clusions. 



Professor Charles S. Ray, assisted by G. H. 

 Lewes, student, and J. Graham Brown, M. D., 

 has pursued an investigation of the blood-press- 

 ure aud its variations in the arterioles, capilla- 

 ries, and smaller veins. Attempts had been 

 previously made to measure the pressure of the 

 blood in the capillaries by N. V. Kries, whose 

 experiments were made upon the vessels of the 

 human skin, particularly on that part of the 

 distal phalanx of one of the fingers immediate- 

 ly behind the nail. The method he employed 

 consisted in pressing, by means of weights, a 

 small glass plate of known area upon the por- 

 tion of skin selected, and finding the weight 

 required to produce a distinct whitening of the 

 compressed as compared with the surrounding 

 skin. It was assumed, in making these experi- 

 ments, that the pressure which sufficed to cause 

 an evident change in the color of the small 

 area of skin lying under the glass plate, was 

 equal to the pressure of the blood in the capil- 

 laries lying nearest the surface. This method 

 was applied with some satisfaction to the de- 

 termination of the relative values of pressure 

 under varied conditions. Professor Ray sought 

 a more delicate method for the study of the 

 absolute values of the pressure by means of mi- 

 croscopic examinations of the web of a frog's 

 foot. The first observations showed that as 



the pressure to which the portion of tissue ex- 

 amined was subjected was raised, the current 

 of blood through the smaller arterioles lost the 

 equable character which it normally presents, 

 and a rhythmic variation in rapidity, a pulse 

 which could not be detected in the small arter- 

 ies while the tissue was uncompressed, each 

 increase corresponding with a heart-beat, be- 

 came more and more evident. The blood-flow 

 through the capillaries also became more and 

 more pulsatile in character, and, in that part of 

 the capillary plexus which lies nearest the ar- 

 teriole whence the blood came, a temporary 

 arrest of circulation took place when a cer- 

 tain pressure, which was different at different 

 points, was reached. It was also found that 

 the capillaries which first cease to convey blood 

 under these circumstances are not always the 

 same, a fact which can not be easily explained 

 otherwise than by assuming that the relative 

 diameters of the capillaries have changed 

 that some vessels have expanded while others 

 have contracted in the interval between two 

 observation:*. In favorable instances such a 

 change in the diameter of the different vessels 

 can be verified with the help of a micrometer. 

 The small veins, or venous rootlets, show under 

 the application of pressure a diminution of di- 

 ameter, often to one third of the original cali- 

 ber, accompanied with an increase in the flow 

 of blood through their interior. The flow of 

 blood in the veins becomes accelerated with 

 each pulse-wave in the arterioles, and slowed 

 between the beats ; and when the blood no 

 longer advances in the arteriole, the corre- 

 sponding vein or veins become empty or col- 

 lapsed. It has long been known that capillary 

 vessels may present considerable variations in 

 diameter at different times, and these varia- 

 tions have been ascribed to the elasticity of 

 the capillary walls. Professor Ray's experi- 

 ments, however, tend to show that modifica- 

 tions of the intra-capillary pressure, much great- 

 er than those which can normally occur, influ- 

 ence but slightly the caliber of the capillaries, 

 and lead almost inevitably to the conclusion 

 that the capillaries are contractile as well as 

 elastic. To the question whether this con- 

 tractility resides in some anatomically differen- 

 tiated part of the capillary wall, or whether it 

 be a property inherent in the wall as a whole, 

 the answer may be returned that capillary ves- 

 sels may he seen to vary greatly in diameter 

 without any localized contraction or expansion 

 being visible ; that the capillary tube expands 

 or contracts as a whole, its diameter remain- 

 ing equal throughout its whole length. The 

 anaemia or absence of blood which is produced 

 on any part by pressure is followed, when the 

 pressure is removed, by an excess of blood or 

 congestion, which gradually passes away. This 

 phenomenon has been proved not to reside in 

 any reflex action through the cerebro-spinal 

 vasomotor centers ; hence attention is directed 

 to the probability of some peripheral vasomo- 

 tor mechanism by which the degree of dilata- 



