BIOLOGY. 277 



pared with collodion, in front of a very narrow aperture exposed 

 to the light. In this aperture is a glass tube, in which a column 

 of mercury may rise or fall, as in a thermometer. By attaching 

 to the wrist a rubber tube, filled with mercury, in connection with 

 the tube of the apparatus, the beating of the pulse is received on 

 this artificial artery, and the pulsations are transmitted to the 

 recording apparatus. As the column in the tube acts as a screen, 

 liofht can penetrate the aperture only where the column is defi- 

 cient; consequently, the prepared plate becomes black under the 

 influence of light everywhere except at such places as the column 

 intercepts it. As the column rises and falls with each pulsation 

 of the heart, these black lines on the prepared plate, pushed regu- 

 larly forward, will be longer or shorter alternately, and will be 

 successively photographed as being lines perpendicular to a com- 

 mon base, the heart being thus made to register photographically 

 its own pulsations. 



Dr. E. J. Marey, of Paris, had discovered, by his "sphygmo- 

 graph " (see " Ainiual of Scientific Discovery " for 1866-67, p. 307), 

 that the pulse was double in some diseased conditions. This Dr. 

 Ozanam shows to be not the exception, but the general rule, and 

 that, when we place a finger on an arteiy, we receive two, and 

 sometimes three, blows. The natural pulse is double, bounding 

 at once to the top of the scale, and then falling, by two or three 

 motions, to the lower level. The first bound is apparently due to 

 the vigorous contraction of the left ventricle, the second and lesser 

 to the contraction of the right ventricle, and the third (the least 

 apparent) to the contraction of the left auricle, or the elasticity of 

 the arteries. These photographic representations can be so mag- 

 nified as to make them visible across a large amphitheatre. This 

 apparatus may be modified to register the variations of respira- 

 tion, the irregular action of coughing, and similar physiological 

 and pathological phenomena. 



NEW ANESTHETICS. 



From time to time, new anaesthetics are discovered. First, ether, 

 then chloroform and nitrous oxide ; now Dr. Leebach, of Germany, 

 has discovered another, to which he has given the name of 

 chloralhydrat. It is highly spoken of by the medical men abroad, 

 and said to be superior to chloroform in producing a more com- 

 plete state of unconsciousness, while it neither induces feebleness 

 nor leaves any bad effects behind. He has held rabbits from 12 

 to 14 hours under the influence of chloralhydrat, during a part of 

 which time he kept them suspended over the back of a chair ; and 

 as soon as they awakened, they displayed their usual activity, and 

 fed with unimpaired appetite. It has been successfully applied as 

 a sedative in the treatment of the insane. Chloralhydrat resembles 

 chloroform in appearance, but it is not so heavy ; and, being much 

 less volatile than that body, it has a feebler odor. On the tongue, 

 it has a sharp, but not an acrid taste ; and, though it reminds one 

 of chloroform, it gives the sensation neither of warmth nor sweet- 



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