PREFACE. IX 



long ago; but the increasing interruptions incident to 

 a professional life, and the large demand made on us by 

 studies of a practical kind, began at an early period to 

 impede our progress. These hindrances did not diminish 

 as time wore on, nor were they lessened by the fact of the 

 authorship being in the hands of two persons, however 

 cordially united by common views and the ties of friend- 

 ship, or by the necessity for frequent and prolonged 

 conferences which that double authorship entailed. 



Such is the apology we have to offer for the tardy com- 

 pletion of our work. It will, we doubt not, be fully 

 appreciated by candid men who know by experience how 

 multifarious are the calls made upon those who not only 

 are candidates for professional employment in London, 

 but hold also the responsible position of public teachers in 

 a large School and Hospital. 



Were it not, indeed, for the kind and valuable co-opera- 

 tion of Dr. Beale, who is now the sole occupant of the 

 physiological chair in King's College, we should not even 

 yet have been released from our difficulties. Dr. Beale, 

 knowing all our views, and having worked with us on 

 many points, has given us very important assistance in 

 drawing up the concluding chapters of the work. Our 

 warmest thanks are due to our friend and colleague for 

 the patient industry and admirable judgment, with which, 

 stepping out of his proper path of independent investiga- 

 tion, he has carried out our intentions, and enabled us, 



b 



