PHYSIOLOGY. 



757 



and are necessary to the perception of color, 

 of form, and to distinctness of vision. The 

 first kind of sensation is supplied by the ex- 

 citement of the rods of the retina through the 

 chemical disintegration of the " visual purple," 

 which is found in their outer segments. The 

 power of giving rise to the second kind of 

 sensations is confined to the retinal cones 

 which wholly compose the bacillary layer of 

 the fovea centralis, but which relatively de- 

 crease in number, with reference to the rods 

 as we recede from this area. Parinaud de- 

 clares that the increase of sensibility of the 

 retina to small differences of luminosity when 

 the amount of objective light is extremely 

 small, is confined to the area outside of the 

 fovea centralis. This increase of sensibility is 

 proportionately greater toward the more re- 

 frangible rays. 



Dr. H. Virchow has found the eye of the 

 frog to be possessed of a beautiful ciliary mus- 

 cle with lung-fibers, which, as in the case of 

 all other animals, composes the posterior and 

 outer part of the ciliary body. This ciliary 

 body fills out the corner arising from the 

 choroid, which closely adjoins the sclerotic, 

 curving round to the iris at the point where 

 the sclerotic passes into the cornea, and, be- 

 sides the muscle, consists of the pigmentary 

 fold and a network of fibers, the ligamentum 

 pectinatum iridis, which is so little developed 

 in man as hardly to merit any consideration. 



A joint meeting of the Physical and Biologi- 

 cal Sections of the British Association was held 

 for the discussion of color-vision. Lord Eay- 

 leigh acknowledged the interest of both of 

 these sides of science in the matter, and said 

 that the first point established by the workers 

 of the subject was that color-vision was three- 

 fold. To prove this it was only necessary to 

 match colors. Dr. Konig said that one could 

 explain all phenomena of color-perception by 

 supposing that each surface element of the 

 retina consisted of three constituents, each of 

 which, when affected, caused a different color- 

 sensation. On this supposition all the various 

 shades of color were the resultant of three fun- 

 damental sensations originating in those con- 

 stituents. Dr. Michael Foster said that the 

 physiologist's point of view was in antagonism 

 to the physicist's in several radical points. 

 The habit of smoking tended to produce color- 

 blindness in the central field of the red ; we 

 were all more or less color-blind in the out- 

 side of the pupil. The more physiologists 

 knew about the living body, the nearer they 

 grew to the conception of the theory that 

 there were two processes always going on 

 in the body a building up, and a breaking 

 down. In the theory of color-perception, this 

 idea was carried out in the supposition that 

 certain rays of light acting on the retina broke 

 down its substance and produced the sensation 

 of color from those rays, and certain other rays 

 broke down the substance of the retina and 

 produced another sensation of color. 



Eecent investigations concerning the effects 

 of various drugs on the sense of taste have 

 shown that the prolonged application of ice 

 removes the sensibility for all tastes. Cocaine 

 destroys the sensibility for bitter, reducing 

 the sensation to a feeling of contact only, 

 while all other substances can still be tasted. 

 Its effect in this direction is more marked than 

 that of any other drug, though several drugs 

 reduce the sensibility for bitter, and caffeine 

 and morphia diminish the discriminative sen- 

 sibility between different intensities of bitter. 

 Sulphuric acid, in a 2-per-cent. solution, 

 makes distilled water taste sweet, and confers 

 a sweetish taste on a quinine solution at the 

 tip, but not at any other part of the tongue. 

 The experiments seem to suggest the supposi- 

 tion of separate fibers for the conduction of 

 separate taste, analogous with the recently 

 discovered hot and cold points in the skin. 



Experiments by Prof. Valentine indicate 

 that men of delicate smell can sniff a pint of 

 air containing bromine in the proportion of a 

 thirty thousandth of a milligramme, or the same 

 quantity of air impregnated with the two mill- 

 ionth of a milligramme of sulphureted hydro- 

 gen, and can probably detect the 280 millionth 

 of a milligramme of sulphureted alcohol or 

 mercaptan. 



Circulation. De Jager has found it an im- 

 pediment to the investigation of the relations 

 of the circulation that the apparatus, with its 

 tubes, etc., by means of which the research is 

 attempted, are mere dead imitations, and have 

 no qualities corresponding with the elasticity 

 of the living tissue. However much we may 

 desire to express what we observe in the or- 

 ganism in a more concise form in other words 

 to reduce the laws which there obtain to a 

 formula the data required for this purpose 

 have nowhere been collected. Thus, if we 

 wish to express in formulas the laws which 

 govern the circulation of the blood, we ought 

 to know to mention but one factor the co- 

 efficient of elasticity of the living wall of the 

 vessels over the whole vascular system. But, 

 when we wanted to employ such a coefficient, 

 we should find that we knew very little about 

 that of the dead tissue, and still less about that 

 of the living one. Hence we are generally 

 obliged to content ourselves with relative 

 statements, when we wish to give absolute 

 ones. The author, using elastic and non-elas- 

 tic tubes, has made experiments on the effect 

 of condensed and of rarefied air upon the respi- 

 ration and the blood-current. From these he 

 deduces the conclusion that, however we cause 

 the condensed air to act during respiration, 

 it will never be favorable, but always detri- 

 mental, to the blood-current. If, with smaller 

 degrees of the action of condensed air, we ob- 

 tain no effect on the blood-pressure, because 

 the heart compensates the influence by its in- 

 creased action, then greater expenditure of 

 energy is demanded of the heart. If this does 

 not occur, there always ensues a fall in the 



