Vol. II. 



PUBLISHED BY THE ALUMNI ASSOCIATION 

 OF THE COLLEGE OF PHARMACY OF THE CITY OF NEW YORK 



New York, October, 1895- 



No. 10. 



WHAT IS BARK? 



By H. H. RUSBY, M. D. 



This question has recently come for- 

 ward in a way which is liable to occasion 

 some inconvenient discrepancies between 

 usage and authority unless those who 

 constitute our authority shall give due 

 weight to the claims of conservatism and 

 good practice. It is answered in two 

 ways. The first is the practical method 

 of framing a definition based upon the 

 obvious structural characters in which all 

 barks agree, without regard to their 

 origin. This definition, for convenience 

 of discussion, we may designate as the 

 practical one. The other is by beginning 

 at the opposite end and fixing the limits 

 of the bark in accordance with the prim- 

 ary structural element which gives origin 

 to it. This we may designate as the 

 morphological definition. The former 

 method gives us a definition which in- 

 cludes all those structures which have 

 come to be recognized under the name 

 "bark," not only in commerce and every 

 day usage, but in literature as well. The 

 latter gives us one which has the merit 

 of conforming strictly to morphological 



principle, but which it is absolutely im- 

 possible to apply in practice. By it, to 

 illustrate, a Calisaya "bark" taken from 

 the tree at one age will include the whole 

 of the bark; that taken later may contain 

 not one particle of if, and it will be im- 

 possible in practice for any one to deter- 

 mine precisely when this stage has been 

 reached. 



If the growing point of any stem or 

 root yielding commercial bark be exam- 

 ined in microscopical section, it will be 

 found to consist of three portions which 

 are readily distinguishable by slight 

 differences in the cells respectively which 

 compose them. The center is a solid 

 cylindrical mass, known as the plerom. 

 Surrounding this is a hollow cylinder of 

 tissue called the periblem, and still out- 

 side of this a second hollow cylinder 

 called the dermatogen. None of these 

 three structures pertains to the older 

 parts of the stem or root, because as they 

 age they change so greatly as to lose al- 

 most entirely their original characters. 

 It is therefore, not these three parts, but 



