24 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 60 



In these tunnels the temperature is often very high (21 to 30.2 

 C. in the St. Gothard) and almost saturated with moisture. The 

 discomfort, weariness, excessive sweating, loss of appetite, and pallor, 

 which may affect tunnel workers, are, we believe, due to the exces- 

 sive heat and moistness of the atmosphere. That this is so is shown 

 by the experiments of L. Paul and Ercklentz. (See later, p. 53 of 

 this paper.) 



RATS AND C0 2 . 

 By a series of observations made on rats confined in cages fitted 

 with small, ill-ventilated sleeping chambers, we (M. F. and L. H.) 



EXPERIMENTS ON RATS 



have found that the temperature and humidity of the air — not the 

 percentage of carbon dioxide or oxygen — determine whether the 

 animals stay inside the sleeping room or come outside. When the 

 air is cold, they like to stay inside, even when the carbon dioxide 

 rises to 4 to 5 per cent of an atmosphere. When the sleeping 

 chamber is made too hot and moist, they come outside. 



