144 



PRESSURE AND RADIATION 



Mosso and Aggazotti, noting the favourable effects of adding CO2 to inspired 

 air and reduced oxygen pressure, came to the conclusion that mountain sick- 

 ness was ' acapnia ' — i.e., primarily due to deficiency in carbon dioxide — 

 but the real facts are that Paul Bert was right in tracing it primarily to lack 

 of oxygen, produced gradually. Mountain sickness usually begins about 

 6,000 to 7,000 feet, and is more marked at heights of over 10,000, but after a 

 sojourn of one or two weeks the efiects pass away. The physiological effects 

 of high altitudes have been studied by Haldane, Douglas, and others, at a 

 height of 14,000 feet and a barometric pressure of 457, when it was found that 

 though persons became ill within half an hour of arrival, their symptoms were 

 relieved immediately by inhalation of oxygen, and acclimatization took place 

 within eight to ten days. 



The partial pressure of COg in alveolar air had fallen to 27 millimetres, 

 and the carbon dioxide ventilation had increased considerably, and therefore 

 the alveolar oxygen pressure was raised above what it otherwise would have 

 been — i.e., 52 millimetres. 



The arterial oxygen pressure was 35 millimetres above oxygen pressure in 

 alveolar air, and accounted for the disappearance of mountain sickness and 

 for the bright red colour of the lips. On arrival it is little above that of alveolar 

 air, therefore acclimatization depends upon the development of the powers of 

 the epithelium of the lung alveoli to actively secrete oxygen inwards, a power 

 which does not exist during rest at sea-level. 



The haemoglobin is increased in a few weeks' residence to 1 1 5 to 1 54 per cent., 

 as indicated by the Gowers-Haldane scale ; and this slow increase is associated 

 with a slow increase in the total haemoglobin of the body and a slight increase 

 in the blood volume. 



The red bone marrow is increased in amount (as shown by experiments on 

 dogs by Zantz), and there is new formation of red corpuscles and a diminished 

 alkalinity of the plasma for unknown reasons. 



RADIATION. 



Radiation from the sun, of heat and chemical rays, is potentially 

 an important factor in producing pathological conditions in man 

 residing in all climates, but more particularly in the tropics. 



In temperate climates its heat effects have been especially studied 

 by Rubner, Cramer, and Wolpert, who. state that, adding half the 

 number of degress of difference between the register of the black 

 bulb thermometer and that of the shade thermometer to the shade 

 temperature, one obtains a figure which corresponds to the thermic 

 effects of the sun. This calculation in the tropics gives a tempera- 

 ture considerably above that of the body, but the only exact method 

 of measuring the caloric value of radiation from the sun is the 

 pyrheliometer of Angstrom, as used in Manila by Aron. Schmidt 

 estimates the heat effect of the tropical sun as being equal to 2 small 

 calories per square centimetre per minute. 



Now, the animal body having a much higher coefficient of absorp- 

 tion of heat than has the air, is capable of absorbing these rays, 

 and hence of becoming hotter; therefore in this way exposure to 

 the sun tends to make the body hotter and helps in the production 

 of the heat-stroke already considered in the last chapter. 



It is, however, with the chemical rays that we are more concerned 

 in the present section, and as yet there are but few observations on 

 this subject in the tropics. 



The earliest experiments, with a view to ascertaining definitely 



