10 TEMPERATURE FLUCTUATIONS IN THE HUMAN BODY. 



he j unction for the purpose of deflecting a galvanometer would be very slight, 

 so that the heating which depends on the square of the current would be 

 very small indeed. Furthermore, a method may be used which does not 

 involve drawing current from the junction, and thus the error may be entirely 

 avoided. 



Again, the resistance thermometer, as usually constructed for body-tem- 

 perature measurement, consists of a coil of fine wire, inclosed in a metal shell. 

 This construction is necessarily bulky, owing to the fact that a considerable 

 quantity of wire must be used. Moreover, the mass of the thermometer is 

 large, giving more or less lag, and its construction is relatively very difficult. 

 The thermal-junction thermometer, on the other hand, in its simplest but 

 thoroughly practical form, consists merely of a twisted and soldered joint 

 between two fine wires, one of which is insulated, both wires being protected 

 from moisture and mechanical injury by an outside case of thin-walled rubber 

 tubing. It will thus be seen that the thermometer is small and flexible, which 

 not only permits its ready introduction into the deep natural cavities of the 

 body, but also allows it to be covered easily by flesh when used in the shallow 

 artificial cavities; furthermore, its small mass precludes any appreciable lag. 



A third disadvantage of the resistance method is that, in the type of ther- 

 mometer commonly used for body-temperature measurement, the resistance 

 itself is not in very good thermal contact with the body whose temperature is 

 being taken, whereas the thermal connection between the thermal-junction 

 thermometer and the body may be made absolutely ideal. Since no theo- 

 retical demands will be violated if one of the metals of the junction actually 

 touches the body being measured, the junction may be made in the form of a 

 wire of one of the metals soldered to the back of a thin plate or cap of the 

 other and the face of this latter applied directly to the body; in this way the 

 active material of the thermometer may touch the body without even the 

 thinnest layer of isolating material. 



A careful comparison of the advantages and disadvantages of these two 

 methods, considered only in the light of the requirements of these special 

 experiments and not at all with regard to temperature measurements in general, 

 led to the adoption of the thermal-junction method, and this in spite of our 

 previous extended use of the resistance thermometer for body-temperature 

 measurements. The sensitiveness was considered ample, and the disadvan- 

 tages of the occasional observations necessary in reading a second temperature, 

 balancing current, and correcting for stray voltage were regarded as being 

 more than offset by the freedom from heating and the ability to use ther- 

 mometers which were at once small, simple, flexible, and strong. The thermal- 

 junction method has the still further advantage that the thermometers are 

 practically interchangeable without adjustment. 



