Chap. xiv.] MEASUREMENT OF TEMPERATURE. 147 



a case of paralysis) a modification of the instrument 

 is made. The pile is made in two halves, as it were, 

 in a plate form, and is small, so as to be quickly 

 affected. Each half consists of two metals arranged as 

 described, with two binding screws, one connected 

 with antimony, the other with bismuth, and is sup- 

 ported on an insulating handle. The flat surface of 

 one half is laid on a place on one side of the body, 

 and the surface of the other half on the other side of 

 the body. The two halves are connected by a wire 

 through a binding screw of each half attached to the 

 same metal, and from the other screw of each half a 

 wire is taken to the galvanometer. If the absolute 

 temperature of the body is to be determined, one half 

 is immersed in a fluid (say, oil) kept at a constant 

 temperature, and the other half laid on the body. 

 The temperature of the oil can be made pretty near to 

 that of the body to be measured, and this gives 

 greater delicacy and accuracy. To determine the 

 temperature of a tissue of the body (for instance, a 

 muscle) the pile is made in the form of a needle, 

 which can be inserted into the muscle without damage. 

 Bismuth and antimony are too brittle for this, but 

 iron and copper may be used. The needle used by 

 Helmholtz is made of an iron wire, to each end of 

 which is soldered a wire of German silver, of half the 

 length, sharpened at one end to pierce the tissues. To 

 get a stronger effect, several such needles are connected 



o O ' 



by their German- silver extremities. One end is 

 pushed into the tissue to the length of the first junc- 

 tion of silver with iron. Helmholtz used this needle 

 for estimating the difference of temperature produced 

 by muscular contraction. The needle being pushed into 

 the tissue, the deflection is noted, and then the muscle 

 is caused to contract, and any movement of the gal- 

 vanometer is observed. A more exact method is to use 

 two needles, connect them by a wire joining similar 



