viii PREFACE TO THE FOURTH EDITION 



For permission to utilise figures I have to thank the editors of 

 the Quarterly Journal of Experimental Physiology, Professor 

 Stewart of Cleveland, and Professor S. Sisson of the Ohio 

 State University, in addition to those acknowledged in former 

 editions. 



My friend, Dr. Sheridan Lea, F.R.S., has again been good 

 enough to undertake the laborious work of reading all the proofs. 

 His acute critical faculty has been invaluable, and I tender him 

 my warmest thanks. 



F. S. 



London, 



February, 191 2. 



