58 RESPIRATIOxN 



out, ether in low concentrations, or by massive afferent nervous 

 stimuli. On the other hand the threshold is raised by such anaes- 

 thetics as chloroform, morphia, or chloral; and under their influ- 

 ence the alveolar CO2 pressure is raised^^ and the breathing is 

 commonly so much diminished that the arterial blood becomes 

 markedly blue. These facts are of great importance in connection 

 with the use of anaesthetics. Henderson showed also that morphia 

 affects the chemical more than the afferent threshold of the res- 

 piratory center. Rise of body temperature has a marked effect in 

 lowering the threshold.^^ 



"Collingwood and Buswell, Journ. of Physiol. (Proc. Physiol. Soc), XXXV, 

 p. xxxiv, and XXXVI, p. xxi, 1907. 



" Haldane, Journ. of Hygiene, V, p. 503, 1905 ; see also Haggard, Journ. of Biol. 

 Chem. XLIV, p. 131, 1920, 



