344 ANIMAL HEAT. 



For many purposes, it is desirable to employ maximum ther- 

 mometers, i. e., thermometers in which the capillary tube pos- 

 sesses a narrowing at one part, which, while it allows the mer- 

 cury to ascend, prevents its return to the cistern ; so that the 

 instrument, when removed from the part, still shows the tem- 

 perature to which the bulb has been exposed. Maximum 

 thermometers are constantly used for clinical purposes in this 

 country, and are also valuable to the physiologist. 



If it is intended to observe the temperature in the interior 

 of the heart, or in any of the great cavities of the body, the 

 animal must be of large size, and must be curarized. To ob- 

 serve the temperature in the right ventricle, the bulb of a long 

 stemmed thermometer must be introduced through the exter- 

 nal jugular. To observe that of the aorta, or left ventricle, 

 the carotid must be opened. If a large do'g is used, a thermo- 

 meter introduced into the right side of the heart may, if the 

 tube-be long enough, be easily pushed onwards into the vena 

 cava. In the rabbit it is scarcely possible to do this, but it is 

 easy with one of the thermometers mentioned above to mea- 

 sure the temperature of the heart in this animal. 



119. Electrical Measurement of Temperature. If 

 a magnetic needle is set in an oblong quadrangular frame, of 

 which one of the long sides is of bismuth and the other three 

 sides are of copper, the two metals being soldered together at 

 the two junctions in such a manner that the needle can swing 

 freely in a plane at right angles to that of the frame, and so 

 placed that the frame is in the magnetic meridian, it can then 

 be observed that if one of the junctions is warmed, the magnet 

 is made to decline from its normal position the degree of 

 deflection varying with the difference of temperature of the two 

 junctions, and continuing until they again resume the same 

 temperature. The deflection of the magnet indicates that in 

 the quadrangle a current exists, and the direction of the de- 

 flection shows that the current flows from the bismuth to the 

 copper, beginning at the warmer of the two junctions. Similar 

 results are obtained when other combinations of two metals 

 are substituted for bismuth and copper. According to the 

 electro-motive force yielded by each, the metals may be ar- 

 ranged in what is called the thermo-electrical series ; in which 

 series those metals are placed furthest apart which yield the 

 greatest quantity of electricity at their junctions. Bismuth is 

 at one end, antimony at the other ; close to bismuth comes 

 German silver, and close to antimony iron. Iron and German 

 silver yield, therefore, nearly as much electro-motive force per 

 degree of difference of temperature as antimony and bismuth, 

 and are much more workable. Being further apart in the 

 thermo-electrical series than bismuth and copper, they are 

 preferable to those metals on that ground also. 



