PHYSIOLOGY. 



653 



ing these reports is the exhibition of a canvas- 

 hooded camera by Mr. Walter Clark, an artist 

 and amateur photographer. This camera is 

 constructed on the principle of the telescopic 

 packing-cases. A spring throws up and fast- 

 ens the canvas hood. The camera below is in 

 two sections, an upper and under. Each has an 

 aperture admitting light, and the lens has two 

 corresponding positions. The upper aperture 

 is just open, the lower being covered with a 

 black disk, since the sensitive plate is already 

 in position. The upper aperture receives the 

 image, which is reflected on a mirror placed at 

 an angle of 45, and is again reflected on a 

 ground-glass plate in the top. By this double 

 reflection the operator sees the image for the 

 first time right-side up, a valuable improve- 

 ment on the inverted image of the ordinary 

 camera. A button regulates the focus. When 

 the operator perceives his image as he de- 

 sires it, a spring causes the lens to fall to 

 the lower aperature, which is now thrown 

 open, and the automatic shutter previously 

 adjusted regulates the time of exposure. This 

 camera is especially designed for out - door 

 work, and more particularly for taking ani- 

 mals or other objects in motion; since it can 

 be carried in the hand, needing neither tripod 

 nor operator's cloth, and can be adjusted in 

 the fraction of a second. George H. Ripley 

 in turn exhibits his improvement on the au- 

 tomatic shutter for instantaneous views, which 

 permits a longer time for exposure. This is 

 invaluable to the amateur, since, if he is alone 

 and desires a figure in his landscape or inte- 

 rior, by means of an invisible silk thread 

 he can photograph himself. These meetings 

 usually conclude with an address on some spe- 

 cial subject, or with an exhibition of lantern- 

 slides. This gives an idea of the general scope 

 of these societies, which are found in Boston, 

 Philadelphia, Lowell, Haverhill, Cleveland, Co- 

 lumbus, Chicago, and Cincinnati. These socie- 

 ties are all in their infancy. That of Cleveland 

 is composed altogether of young men not yet 

 out of school. As yet, these societies have no 

 journal devoted to their interest; but the 

 "Photographic Times," edited by J. Traill 

 Taylor, with the co-operation of W. J. Still- 

 man and Charles Ehrman, gives much consid- 

 eration to amateur photography. 



PHYSIOLOGY. Physiological Experimentation. 

 An indication of the direction in which physio- 

 logical experiment may be pursued to advan- 

 tage in the future is given by Prof. Tyndall in 

 considering those diseases of which a single at- 

 tack secures immunity against all future attacks. 

 This phenomenon, hitherto unexplained, maybe 

 accounted for under the germ theory of disease 

 by supposing the system the soil in which the 

 parasite is developed to be exhausted by the 

 first crop of some ingredient necessary to the 

 growth and propagation of the microbe. M. 

 Bouley has drawn attention to the fact that, 

 in the experimental cultivation of the micro- 

 scopic plant Aspergillus niger by M. Kaulin, 



the omission of potash from the culture-liquid 

 sufficed to make the produce fall to one twen- 

 ty-fifth of the amount collected when potash 

 was present. The addition of an infinitesimal 

 amount of a substance inimical to the life of a 

 plant is attended with still more striking re- 

 sults. Thus, the addition of one part in 1,600,- 

 000 of nitrate of silver entirely stops the growth. 

 Now, supposing the Aspergillus to be a human 

 parasite a living contagion capable of self- 

 multiplication in human blood, and of so alter- 

 ing the constitution of that liquid as to produce 

 death ; then, the introduction into the blood of 

 a man weighing sixty kilogrammes of five milli- 

 grammes of nitrate of silver would insure, if not 

 the total effacement of this contagium, the neu- 

 tralization of its power to destroy life. From 

 such facts as this we may foresee that in anti- 

 cipation of the assault of infectious organisms, 

 the experimenter of the future will try to in- 

 troduce into the body substances which, small 

 in amount, shall so affect the blood and tissues 

 as to render them unfit for the development of 

 the contagium ; and, subsequent to the assault 

 of the parasite, substances which shall effectu- 

 ally stop its multiplication. Dr. Polli, of Mi- 

 lan, has already found some alkaline sulphides 

 that seem to be good against certain fevers and 

 small-pox, and Crudelli has found arsenic help- 

 ful against the malaria of the Roman Cam- 

 pagna. To enable us to use these remedies 

 safely and with some assurances of success, 

 experiments must be made of their effects on 

 different groups of individuals, and these indi- 

 viduals must be animals susceptible to the in- 

 fection and to the counteracting applications. 



The Nervons System. The effects of the extir- 

 pation of the cerebrum in rabbits was consid- 

 ered by Prof. Munk in an address before the 

 Physiological Society, a part of which was de- 

 voted to the difference in the results obtained 

 in his own experiments and those which Prof. 

 Christian! had reached in his researches. In 

 his own most successful experiments, after re- 

 moving the cerebrum, he had observed in rab- 

 bits, just as in other vertebrates, birds and 

 frogs, a state of depression lasting for a longer 

 or shorter period, to as long as several hours, 

 a state in which they lay apathetically, taking 

 and keeping whatever position might be im- 

 posed upon them. From this state they re- 

 covered to go through, first, interrupted and 

 apparently spontaneous movements, which yet, 

 on closer inspection, proved to be reflex move- 

 ments. These, again, were followed by a quick- 

 ened reflex excitability, which finally was suc- 

 ceeded by convulsive movements, a kind of 

 running stage, which, in from twenty-four to 

 fifty hours after the operation, issued in the 

 death of the animal. Prof. Christiani, on the 

 other hand, after removing the cerebrum, in 

 no case observed a state of depression, but his 

 excerebrated rabbits all acted like normal ones. 

 They moved about, sprang, ran, etc., during 

 the first twelve hours, at least, after the opera- 

 tion. Prof. Munk ascribed these differences to 



