652 



PHYSIOLOGY. 



this, instead of increasing the knee jerk, renders it 

 difficult or impossible to obtain it. Dr. Russell be- 

 lieves with others that the spinal centers are nor- 

 mally under a certain degree of restraint by cerebral 

 centers, and that what is called re-enforcement is 

 really removal in some degree of this inhibition, a 

 removal which may be effected by diverting the 

 patient's attention to some other act. Removal 

 also of one hemisphere in an animal causes in- 

 creased activity of the opposite knee jerk. Further, 

 the return of the knee jerk in Kramer's case of pro- 

 gressive paresis is accounted for by supposing the 

 inhibition lessened as the result of progressive cere- 

 bral degeneration, so that there comes a time when 

 the spinal centers are so far freed from inhibition 

 that the few remaining fibers in the posterior col- 

 umns are sufficient for the purpose of carrying a 

 stimulus which was formerly ineffective because of 

 the inhibition from above. 



The experiments of Gotch and Macdonald on the 

 relation between temperature and excitability in 

 nerve and muscle indicate that the rule that in- 

 creased excitability occurs with increased tempera- 

 ture is not invariable, since such tissues do not be- 

 come more excitable to all forms of stimulus as the 

 result of an elevation of temperature. In each case 

 the nature of the tissue and the nature of the 

 stimulus require to be investigated. 



The results of the researches of Hills (Research 

 Scholarship of the Grocer's Company) on the phys- 

 iology and pathology of the cerebral circulation 

 go to sustain Kellie's view that the volume of blood 

 in the brain under physiological conditions varies 

 but little; and, further, the author has satisfied 

 himself that there are no. or few vasomotor nerves 

 distributed to the cerebral vessel a view which the 

 " Lancet" regards as requiring confirmation. 



Experiments by R. Hunt, contradicting the com- 

 monly accepted opinion of Baxt, go to show that 

 the inhibitory and accelerator nerves are to be re- 

 garded as purely antagonistic, and that the result 

 of stimulating the two together is approximately 

 the algebraic sum of the effects produced by stimu- 

 lating them separately. In no case did one nerve 

 completely overcome the effect of the other, though 

 the two were stimulated for periods as long as twelve 

 minutes. 



T. Hough has .observed that when the inhibitory 

 impulses attained by stimulation of the vagus nerve 

 are just strong enough to bring the heart of the 

 dog to rest the duration of the standstill is not so 

 long as with stronger stimuli ; but that a very 

 slight increase of stimulus above this point pro- 

 duces a standstill which is not lengthened by any 

 further strengthening of the inhibitory impulses. 



In the case of a patient who died in convulsions 

 with which he had been suddenly seized no signifi- 

 cant abnormality was found by Dr. Munro, of Glas- 

 gow, in any organ but the brain. When the dura 

 mater was removed it was found to be lined on the 

 left side by an adventitious membrane about as 

 thick as itself, firm and adherent, although it could 

 be stripped off. The membrane was reddish and 

 was not adherent to the pia-arachnoid except in the 

 region of the left olfactory bulb. There was no 

 evidence of haemorrhage to the naked eye, and the 

 membrane appeared to be of recent development. 



In the course of a description of the effects of the 

 division of one inferior peduncle of the cerebellum 

 J. S. Risien Russell has shown that in the disorders 

 of equilibration that result the direction of rotation 

 is always toward the side of the lesion. 



The ciliary ganglion has been regarded some- 

 times as a spinal, at other times as a sympathetic 

 structure. The results of experiments by Dr. Apo- 

 laut, of Berlin, upon cats seem to place it in the 

 sympathetic system. 



Special Senses. The number of visual units 

 existing in the human retina is discussed in a paper 

 by Prof. Konig before the Physical Society of Ber- 

 lin. The acuteness of vision was measured by the 

 distance at which a grating made of regular recti- 

 linear wires begins to appear wavy. Starting at the 

 fovea, it diminishes toward the periphery, and in such 

 a way that the curves of equal visual acuteness form 

 concentric ellipses. The area of each retinal field 

 by which two wires are seen as two increases to- 

 ward the periphery. If such a field be called a 

 visual unit, then their total number for the whole 

 retina is 50,000. If it be assumed that each unit 

 can perceive. 3 kinds of color, of which the result- 

 ing impulse is conveyed to the brain by a separate 

 nerve fiber, then there must be 150,000 fibers in the 

 optic nerve. As a matter of fact, histologies esti- 

 mate the number at from 400,000 to 500,000. The 

 author further discussed the experiments he had 

 made in connection with Dr. Zumpf, which showed 

 that objects of different color must be observed at 

 different depths in the retina. The difference of 

 these depths for red and blue rays proved so great 

 that one lay in the pigment layer, which is hence re- 

 garded as a sensory organ. An English anatomist 

 has described the existence of spherules in this 

 layer united to a nerve plexus from the rod and 

 cones. Prof. Konig finally gave an historical retro- 

 spect of Purkinje's phenomenon, in which two col- 

 ored (red and blue) fields of equal luminosity as seen 

 by daylight appear unequally luminous at twilight, 

 the red disappearing much sooner than the blue. 

 After this phenomenon had been studied by a whole 

 series of observers and its importance insisted upon, 

 Prof. tiering had recently found that it is an ex- 

 ceptional phenomenon. It can only be observed in 

 dark surroundings; in daylight and bright sur- 

 roundings the differently colored fields remain 

 equally luminous, while the intensity of their illu- 

 mination is reduced down to a point at which color 

 perception ceases. Prof. Konig had satisfied him- 

 self of the truth of this observation, and thus Pur- 

 kinje's phenomenon has now lost all its supposed 

 significance. 



An experiment made by M. Charles Henry with 

 a new pupilometer upon the action of light on the 

 iris proves that there is almost always a dilatation 

 of the pupil when the iris is withdrawn from the 

 light. The variations of the dimensions of the iris 

 are much less when it is the iris alone that is sub- 

 jected to light than when the iris and the retina are 

 influenced together. Another experiment indicates 

 that this action of light upon the iris is due, in part 

 at least, to a reflex of cerebral origin ; but, on the 

 other hand, we do not yet possess sufficient knowl- 

 edge of the anatomy of the iris to enable us to say 

 whether these variations are due to the direct ac- 

 tion of light on muscular elements, as supposed by 

 Brown-Sequard, or to the action of nervous centers 

 as yet unknown belonging to the iris. 



The visual purple of fishes is described by Dr. 

 Abelsdorff, of Berlin, as showing a maximum in its 

 absorption spectrum differing from that in the simi- 

 lar spectrum obtained from amphibia, birds, and 

 mammals. A solution of visual purple obtained 

 from fish exhibited by the author, which was at 

 first of an obvious violet color, became speedily yel- 

 low under the action of light, and then finally and 

 very slowly colorless. By treating fish eyes with 

 alcohol and formalin the author had obtained prep- 

 arations which showed the retina of a brilliant pur- 

 ple color as looked at anteriorly. 



Miscellaneous. It is pointed out by Dr. Laza- 

 rus Butler that before the laws of osmosis, deduced 

 from the final osmotic pressure, freezing point, etc., 

 can be applied to the explanation of biological prob- 

 lems, it is necessary to determine whether the initial 



