PHYSIOLOGY. 



673 



is transmitted to the central terminus of the 

 filament in the cerebral retina, where it is 

 fully evolved into such a condition as to be 

 transferred into an automatic form of percep- 

 tion by an action upon some unknown contigu- 

 ous perceptive nerve-elements. 1 ' Suppose the 

 nerve-points to be exposed to a beam of light 

 of, say five hundred trillion beats per second, 

 the average response to the sensation thus 

 produced upon healthy tissue would be what 

 is known as red. Each impinged point would 

 excite a sensation equal to a specific energy 

 equivalent to red. If the undulations are six 

 hundred trillions to the second, the sensation 

 would produce a specific energy giving the 

 response of green. And if a beam of light of, 

 say seven hundred and thirty-three trillions 

 of vibrations per second he thrown upon the 

 same sentient points, violet would be given as 

 the answer. "Each and every optic-nerve 

 fiber tip has a receiving power equal to its in- 

 dividual strength. Each and every healthy 

 optic-nerve filament transmits to the color 

 center for recognition nerve-energies equal to 

 as many special sensations as its peripheral tip 

 is capable of receiving. The innumerable 

 quantities of nerve-filaments placed side by 

 side on a sheet or membrane serve to give 

 a greater field and allow many colors to be 

 seen at one and the same time, thus making 

 our every-day and momentary pictures." 



The feeling of cold produced in the forehead 

 on the application of menthol for relief from 

 headache has been assumed to he a result of 

 the cooling of the skin consequent on evap- 

 oration. On the other hand, the feeling of 

 cold produced in the mouth by mouth- washes 

 containing mentha has been supposed to be due 

 to an astringent effect of this substance. Not 

 believing that these explanations were correct, 

 Dr.Goldschneider experimented with a solution 

 of menthol in lanoline, which was rubbed into 

 circumscribed places of the skin. Measured 

 with the thermometer, those places showed 

 an increase of temperature after the rubbing, 

 yet there was a decided feeling of cold ; and 

 this feeling was also observed when the place 

 where the solution was rubbed in was protect- 

 ed against evaporation by a watch-glass. The 

 feeling in question could therefore proceed only 

 from a direct stimulation of the nerves convey- 

 ing the sensation of cold. If of two places on 

 the forehead exactly corresponding to one an- 

 other, the author observed, the one were rubbed 

 with menthol salves and the other not, bodies 

 which before had produced no impression, being 

 indifferent, would now be felt as cold by the 

 part of the skin where the rubbing was made, 

 whereas there would be no perceptible impres- 

 sion on the other part. Hence Dr. Goldschnei- 

 der concludes that menthol produces a specific 

 influence on the nerves of cold which are dis- 

 tributed with especial copiousness en the fore- 

 head. 



Circulation. Experiments on the relation 

 between the curve of distention of elastic tubes 

 TOL. xxvn. 43 A 



and the rate of the pulse- wave in the same, 

 have been made by Dr. Grunmach with various 

 gutta-percha tubes and with the aorta of 

 horses. The internal pressure being varied 

 from to 200 mm. of mercury, the alteration 

 of volume of the tubes, and the rate of trans- 

 mission of the pulse-wave were measured. The 

 results showed that the rate of the pulse-wave 

 is most markedly dependent upon the disten- 

 tion-curve or coefficient of elasticity of the 

 tube. This coefficient is, however, very variable 

 with different tubes. The behavior of a horse's 

 aorta approximated to that of an India-rubber 

 tube wrapped with linen. The thickness of 

 the walls of the tubes and the size of their 

 lumen was very slightly, if at all, altered by 

 the varying pressure, and their influence upon 

 the relationship of pressure and rate of pulse- 

 wave was quite subordinate. 



The specific gravity of the blood in health, 

 according to the investigations of Mr. E. Lloyd 

 Jones, is highest at birth, reaches a minimum 

 between the second week and the second year, 

 and rises gradually to a point attained in the 

 male between the ages of thirty -five and forty- 

 five; and in the female after the climacteric. 

 As a rule, it tends to be higher in the male 

 than in the female; and in the female the 

 child-bearing period is marked by a fall. In 

 pregnancy it is slightly diminished, though it 

 still remains well within healthy limits. The 

 immediate effect of mixed food is to cause a 

 fall ; if alcohol is taken this fall is not ob- 

 served. Exercise, if gentle and not too pro- 

 longed, causes a fall ; if pere piration becomes 

 well marked the specific gravity rises, as it 

 does when violent exercise is taken. The con- 

 ditions of the circulation in the affected part 

 modify the specific gravity of the blood circu- 

 lating through it. It is always high in a pas- 

 sively congested part. It varies also in differ- 

 ent parts of the body. It exhibits a certain 

 diurnal variation, tending to fall during the 

 day and to rise at night. 



The influence of extremes of temperature 

 on the color of the blood has been described 

 by Prof. Falk, who found that temperatures 

 of C. and below lead to the color of the 

 blood becoming bright red by causing the oxy- 

 gen of the air to be more readily fixed and 

 more stably retained by the corpuscles than is 

 the case at ordinary temperatures. If, how- 

 ever, the blood has stood exposed to the air 

 until putrefactive changes have set in, the ac- 

 tion of cold no longer makes it brighter in 

 color. Other experiments have shown that in 

 animals killed by low temperatures, the blood 

 is bright red, not only in the peripheral parts, 

 but also in the heart and great vessels. Also 

 in human beings frozen to death the blood 

 even in the heart is sometimes observed to be 

 bright red, although in most cases only the 

 blood of the peripheral parts presents this ap- 

 pearance; probably death has ensued from 

 freezing only in cases presenting the first of 

 these two appearances. 



