64 SECRETION. 



(3) Clothing and the protection afforded by houses, and the ele- 

 vation of the temperature of air indoors by fire, are factors in the 

 regulation of the body-temperature. 



What is meant by heat-centres in the brain? 



There are reasons for believing that there are nervous centres 

 exciting the heat-production in the tissues (thermogenic centres), 

 and centres which check the metabolism of tissue, and thus con- 

 trol the temperature (inhibitory heat-centres). This is not entirely 

 proven, nor can these centres be localized. We do know that the 

 innervation of a part is necessary for the maintenance of its 

 warmth, aside from vaso-motor causes for alteration of tempera- 

 ture. 



What are the extreme limits of body-temperature found in life ? 



In ordinary pathological conditions the temperature does not 

 remain long at a point below 95 F. or above 105 F. without 

 fatal results. Under extreme conditions of prolonged exposure to 

 cold and the algid stage of cholera recovery has occurred after a 

 bodily temperature as low as 75 F. On the other hand, in some 

 cases of extreme fever, as from sunstroke, recovery has been noted 

 after a temperature of 110-112 F. has been observed. 



SECRETION. 

 What are secretions? 



Materials separated from the blood by the cells to serve some 

 further purpose in the animal economy. These secretions are for 

 the most part elaborated by the glands, though the mucous and 

 serous membranes act in this capacity as well. Examples of 

 secretions are found in milk, bile, gastric juice, tears, etc. 



What are excretions? 



Materials which are separated from the blood by cell-activity 

 and discharged from the body, being either useless or harmful if 

 retained ; e. g. urine, sweat. 



What is the function of the serous secretions ? 



Lubrication of surfaces in which friction is undesirable. Such 

 conditions are found in the pleural cavity, peritoneum, tunica 

 vaginalis, and in a similar way in the synovial cavities of joints, 

 tendon-sheaths, etc. 



