258 



GENERAL PHYSIOLOGY 



not given off to the medium by conduction or radiation, is proved 

 by the fact that bees in their hives can produce temperatures of 

 from 30° to 40° C. Even plants can raise their temperature above 

 the temperature of the surroundings, as can be determined thermo- 

 metrically, especially in sprouting and in vigorous growth where 

 the metabolic processes are particularly active. Sachs was able to 

 determine with a thermometer a rise of temperature of 1'5° C. in 

 peas which were allowed to sprout in a funnel under a bell-jar 

 (Fig. 114). Very remarkable temperatures have been observed in 

 the spadices of the peculiar Aro'ideae during 

 their development : here not rarely a rise of 

 15° C. is found. A rise which under favour- 

 able conditions can amount to more than 

 14° C. is produced also by yeast-cells in the 

 fermentation of sugar solutions. 



For the determination of delicate changes 

 of temperature, especially in the tissues of 

 poikilothermal animals, the rough method of 

 measurement of temperature by the thermo- 

 meter is not sufficient, and hence the finer 

 method of thermo-electric measurement has 

 been employed. As is well kno^vn, in a 

 thermo-electric element, which consists of 

 two pieces of different metals soldered to- 

 gether at one end (the best metals are German 

 silver and iron, or antimony and bismuth), 

 an electric tension is produced by slight 

 warming of the soldered place. If the two 

 free ends of the metals be joined by a wire so 

 that a closed circuit exists, an electric current 

 can be led off from them, the presence of 

 which is shown by the deviation of a mag- 

 netic needle in the vicinity. For the demon- 

 stration of very feeble currents especially 

 sensitive apparatus is needed, such as the 

 multiplier and the galvanometer, the mag- 

 nets of which are moved by very delicate 

 currents. The multiplier consists of a suspended and easilj^ 

 moved astatic system, i.e., two horizontal magnetic needles 

 which are fastened together parallel one above the other, so that 

 the north pole of the one lies above the south pole of the other. 

 In the region of the lower needle the wire of the circuit is wound 

 into a coil consisting of an exceedingly large number of turns, so 

 that when the current goes through it, all the individual turns 

 tend to deviate the needle in the same direction. The upper 

 needle hangs above a disc divided into degrees, so that here the 

 deviation of the needle can be measured (Fig. 115). In the 



Fig. 114. — Apparatus for 

 demonetrating the rise 

 of temperature in tlie 

 sprouting of peas. Under 

 a bell-jar is a funnel con- 

 taining sprouting peafi, 

 into which projects a 

 thermometer. .-(After 

 Sachs.) 



