viii PREFACE. 



The writer wishes, in conclusion, to express his 

 sincere thanks to Prof. Francis Delaficld, to whose 

 wise counsel and unwearied assistance in many 

 matters requiring a wider experience than his own, 

 he is greatly indebted. 



T. M. P 



LABORATORY OF THE ALUMNI ASSOCIA- 

 TION OF THE COLLEGE OF PHYSICIANS 

 AND SURGEONS. 



NEW YORK, May, 1881. 



