378 THE POPULAR SCIENCE MONTHLY. 



Quitting the quality of the power given to us to start with, we are 

 next dependent upon the influences derived from the external or sur- 

 rounding conditions to which Ave hecome exposed. Light, air, what we 

 eat and drink, or what in any way gets into the system, temperature, 

 exercise of mind and body — in short, the conditions under which we 

 live — all exert their influence in favoring or otherwise a natural pas- 

 sage through life. Within us, operations forming a part of the opera- 

 tions of Nature proceed, but these operations are influenced by — owe 

 their activity, indeed, to — the surrounding conditions, and thus it is 

 that upon these surrounding conditions depends whether a natural 

 course is run or not. Under the same law, these surrounding con- 

 ditions may exert a modifying influence in this or that particular direc- 

 tion upon the operations that are proceeding, and by long continuance 

 in force may lead to the establishment of a more or less modified state 

 as a part of our nature, in accordance with the Darwinian principle of 

 natural selection. This matter — the modifications for good or bad, 

 wrought in our nature by the influence of external conditions — em- 

 braces a wide field of study, and comprehends nothing less than the 

 possession of a knowledge of the varied operations, with the laws de- 

 termining them, going on around us, in order that we may understand 

 the manner in which they are brought about. It is a vast subject, but 

 the mind of man has already done much, and there is reason to think 

 will do much more, toward penetrating it ; and, as with the amount of 

 knowledge acquired, power is possessed — that is, the power of arrang- 

 ing conditions or operations so as to render them subservient to the 

 production of a desired effect — man stands in the position of an increas- 

 ingly powerful agent in the realm of Nature. Must not the mind itself, 

 then, through which this is accomplished, be reckoned as a power — a 

 great power among the powers of the universe ? In our special de- 

 partment as medical practitioners, it falls to us to apply the power 

 which knowledge gives us toward preventing unnatural conditions of 

 the body from being allowed to become developed, and toward bring- 

 ing the unnatural back into the natural state — in fact, toward aiding in 

 carrying life on in a natural manner through its ordinary term of ex- 

 istence. — Lancet. 



VINEGAR AND ITS MOTHER. 



By FEEDERIK A. FEENALD. 



" QjWEET as sugar" and "sour as vinegar" are among the most 

 k_J common comparisons in our language, and the two substances 

 chosen to represent these opposite qualities are popularly deemed as 

 unlike as they can well be. Yet it is one of the marvels of chemistry 

 that the sourest substance with which we are familiar is made from 

 the sweetest. By the action of a ferment, the sugar in some sweet 



