808 SEC. 18. BIOLOGY. 



of the chamber is perforated by a metallic tube, of 30 mm. long, 4 mm. 

 wide, for the entrance and escape of gases. To investigate the influence of 

 electric currents on the object, which is placed in the moist space filled with 

 air or any other gas, a lid of ebonite is used ; it is furnished with two metal 

 binding screws in which the wires are fastened. From each of the screws on 

 the inferior surface of the lid a movable platinum wire conducts to the drop. 



In order to examine the influence of changes of temperature and of higher 

 temperatures a similar lid is used, but furnished with a single platinum wire 

 combining the two screws and passing through the drop. This wire is heated 

 by a galvanic current. By modifying the intensity and duration of the 

 current, fluctuations of temperature of any desired magnitude and velocity 

 can be produced in the preparation. To prevent evaporation of the drop 

 when heated it is also covered underneath with a glass. 



(Onderzoekingen gedaan in het physiologisch laboratorium der 

 Utrechtsche Hoogeschool. Tweede Reeks, I. 1868, p. 140, &c., PI. VIII.) 



3952. Set of Tympana for receiving the impressions of 

 movements and communicating them by air-transmission to the 

 cardiograph (modified stethoscope of Konig). 



Prof. Danders, Utrecht. 



On the rim of a hollow brass basin are fastened two elastic membranes, the 

 outer membrane convex, the inner membrane concave, owing to the air be- 

 tween them. Close to the rim of the basin a tube a conducts into the space 

 between the two membranes. In the centre of the basin (or elsewhere) 

 a tube b conducts into the space between the basin and the inner mem- 

 brane. On sucking at the latter tube, 6, the inner membrane falls against the 

 basin ; on closing now the first tube a, and ceasing to suck, the space between 

 the two membranes assumes the form of a bi-convex lens. With two india- 

 rubber lengths fastened on the tubes c, for the ears, these instruments are 

 excellent stethoscopes. 



The special office of the tympana is to receive the impressions of move- 

 ments (beating of the heart, pulsation of the carotid artery, respiration, &c.) 

 and to communicate them by air- conveyance to the cardiograph. (Compare 

 the curves.) 



3953. Chronoscopic Tuning: Forks. Set of 4 tuning fork*. 

 with 10, 25, 50, and 100 vibrations per second, to be used as 

 chronoscopes ; they have a long, very pliable, flat spring, movable 

 in its plane and perpendicularly on it, in order to be easily applied 

 to the cylinder. P r f- Donders, Utrecht. 



3954. Direct" registering Levers (large size) attached to 

 lead wires. Prof. Donders, Utrecht. 



Very light registering levers with a pin (aluminium or cork) resting on 

 the moving object (a contracting muscle, fontanelles, &c.). Two levers, one 

 with a doubly bent pin, fixed on the same stand, can register two movements 

 on the same cylinder, one immediately below the other (the contractions of 

 the auricle and ventricle of the heart of a frog). Comp. Nuel. Onderzoe- 

 kingen gedaan in het physiologisch laboratorium te Utrecht, Ser. 3, T. 11. 

 p. 292, and Pfliiger's Archiv. B. ix. S. 86. 



3955. Apparatus for verifying the Transmission of 

 Movements by Air, an india-rubber tube, and a Marey's 

 Cardiograph. Prof* Donders, Utrecht. 



On a horizontal revolving axis is fixed an eccentrically ground brass disc, 

 which moves a metallic spring placed underneath it. This spring registers 



