PREFACE TO THE SECOND EDITION. 



THE cordial reception and favorable criticism accorded 

 the first edition of this little book, prompted its author 

 to exert every effort to eliminate such defects as were 

 discovered by his reviewers, to accept the kindly sugges- 

 tions of several of his readers, and, without considerably 

 increasing its size, to introduce such new matter as 

 would bring its contents up to date and increase its use- 

 fulness. 



It is hoped that all this has been accomplished, and 

 that future readers may find the book a reliable guide in 

 the much-neglected field of biological science that borders 

 upon and often overlaps the "Institutes of Medicine." 



JOSEPH MCFAKLAND. 



PHILADELPHIA, PA., 

 November, 1913. 



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