Recording Thermometers for Clinical Work. 553 



on which the thermometer coil itself was wound, so that any 

 changes in its resistance were due to change o£ temperature 

 ■of the thermometer, and were allowed for when the thermo- 

 meter was calibrated. This construction was adopted in 

 order to avoid the necessity of applying any correction for 

 change of temperature of the resistance box ; but it is open 

 to the objection that it makes the thermometer rather less 

 sensitive, and doubles the heating effect of the current. The 

 sensitiveness of the celluloid rectal thermometer, though only 

 about half as great as that of the Herseus thermometer, was 

 ample for records of long duration. The heating effect of 

 the current was only a tenth of a degree, and did not intro- 

 duce any appreciable error, since it remained practically 

 constant, and was allowed for in the calibration, in which 

 the same current was employed. 



A more important source of systematic error would lie in 

 variation of E.M.F. of the battery during a long continued 

 run. But unless the storage cells employed were nearly run 

 down, this would not be likely to amount to more thar 

 1 per cent, of the galvanometer deflexion, or two or three 

 hundredths of a degree, since the galvanometer deflexion 

 •corresponds only to the small difference from the balance 

 point which is in the neighbourhood of 37° C. The zero of 

 the galvanometer and the deflexion per degree would of 

 course be tested, and, if necessary, adjusted daily. 



(3) Surface or Axillary Type. — A tube form of thermo- 

 meter is not very suitable for this purpose, since the contact 

 between the thermometer and the skin is necessarily imper- 

 fect. It is desirable to give the thermometer as large a 

 surface as possible, in order to diminish the heating effect 

 of the current, and at the same time to make the bulb flexible 

 and thin, so as to conform approximately to the contour of 

 the surface to which it is applied. The first thermometer 

 of this type which I constructed for Prof. Adami of Montreal 

 in 1897, was made bv sticking a thin bolometer grid of 

 platinum foil on to a thin sheet of celluloid photographic 

 film. This satisfied the required conditions very perfectly, 

 but the bolometer grid was excessively fragile (unless its 

 resistance were made unduly low), and was also difficult to 

 attach securely to the leading wires. The substitution of 

 fine wire for the foil greatly facilitated the construction and 

 adjustment, and was found to make little, if any, difference 

 to the sensitiveness. In any case it is most important that 

 the thermometer should be fairly robust, as it has to undergo 

 somewhat rough usage. In my experience nothing answers 

 so well as celluloid film for the insulating material. The 



