ACTION OF THE TROPICAL SUN. 117 



between it and the brain. The blood vessels of the brain are very hyper- 

 semie; fresh, small hsemorrhages are found in several places on the basal 

 side of the frontal lobe. 



There can be no doubt but that the changes in the brain and the lesions 

 of the heart described above were fresh and characteristic of the efEects 

 of the sun. (See Plates I and II.) 



The following seems to me to be the most probable interpretation of our 

 observations on monkeys, dogs, rabbits, and cats. The heat radiated from 

 the sun warms the body tissues more rapidly than can be compensated for 

 by the regulatory organism of the body. The tissues and the blood in- 

 crease in temperature to a point higher than is compatible witli life. Ap- 

 parently the organs most susceptible to this increased heat effect are the 

 brain and heart. It is undecided whether the lesions in the brain or 

 heart are the most essential in causing death. 



The most important fact shown by these experiments is that the outer 

 parts of the body are heated by the sun to a greater extent than the inte- 

 rior. Therefore, I next endeavored to ascertain the effect of the rays of 

 the tropical sun upon the temperatures of thp skin of man. 



I have not found any account of experimental work done in this line. 

 Diiubler -^ discusses the skin temperature and shows the necessity of investigations 

 in the Tropics. The only fact which need be mentioned here is a statement by 

 Schilling. This investigator placed a thermometer between the teeth and cheek 

 in the mouth of a man. In the room, the thermometer showed 36°'.6. The man 

 exposed his face to the sun when the sunshine thermometer registered 5.5°, the 

 thermometer in his mouth rose to 37°. 05. 



THE TECHNIQUE OF THE EXPERIMENTS. 



Mercury thermometers, even if especially constructed for taking the 

 skin temperature, are not suitable for this work because it is impossible 

 to protect such instruments against the radiation of the sun. The 

 only method suited to taking exact measurement of skin temperatures 

 is thermoelectric, as it has been applied by Kunkel ^^ and Eubner, 

 Kisskalt,-^ Eeichenbach, and Heymann -* in the study of the normal 

 skin temperature in men. The greatest difficulty to be overcome in 

 the construction of such an apparatus for our studies was to keep the 

 secondary place of junction of two metals at a constant temperature, 

 even in the sun, and to avoid disturbing currents produced by changes 

 in temperature of any junction between two different metals in any part 

 of the circuit outside the thermocouple proper used for the measure- 

 ments. 



-^ Die Grundziige der Tropenhygiene, Berlin, 1900. 

 '■Ztschr. f. Biol. (1889), 25, 5.5-91. 

 ■'Arch. f. Hyg. (1909), 70, 17-39. 



-* Ztsclir. f. Eyg. u. InfectionskranJch. (1907), 57, 1-22. 

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