THE CHEMIST AS A CONSTRUCTOR. 80 1 



provided, etc. The digestive juices contain essentially ferments 

 which act only under definite conditions of chemical reaction, 

 temperature, etc. 



The changes wrought in the food are the following : Starches 

 are converted into sugars, proteids into peptones, and fats into 

 fatty acids, soaps, and emulsion; which alterations are effected 

 by ptyalin and amylopsin, pepsin and trypsin, and bile and pan- 

 creatic steapsin, respectively. 



Outside the mucous membrane containing the glands are mus- 

 cular coats, serving to bring about the movements of the food 

 along the digestive tract and to expel the faeces, the circular fibers 

 being the more important. These movements and the processes 

 of secretion and so-called absorption are under the control of the 

 nervous system. 



The preparation of the digestive secretions involves a series of 

 changes in the epithelial cells concerned, which can be distinctly 

 traced, and takes place in response to nervous stimulation. 



These we regard as inseparably bound up with the healthy life 

 of the cell. To be natural, it must secrete. 



The blood-vessels of the stomach and intestine and the villi of 

 the latter receive the digested food for further elaboration (absorp- 

 tion). The undigested remnant of food and the excretions of the 

 intestine make up the faeces, the latter being expelled by a series, 

 of co-ordinated muscular movements essentially reflex in origin. 



■»*» 



THE CHEMIST AS A CONSTRUCTOR. 



Br W. BEENHAEDT. 



ONE of the most attractive branches of modern chemistry 

 comprises the artificial preparation of compounds existing 

 preformed in nature, or, in other words, the imitation of the 

 works of creative power. Synthesis, as this section of chemical 

 investigation is called, although it has already attained a consid- 

 erable degree of success, is of but recent origin compared with 

 analysis, or those researches by which we become acquainted with 

 the composition of the products of nature, and of what we derive 

 from them by industrial processes. It is an indispensable con- 

 dition, before learning how to compound a body, to know what 

 are its constituents, what their properties are, and by what agents 

 they are most liable to be brought into combination with each 

 other. Therefore, synthetical processes could only be founded 

 upon the results of analytical investigations. It is chiefly to the 

 thorough knowledge of the properties and affinities of the seventy 

 so-called elements that we owe the innumerable discoveries which 



VOL. XXXV. — 51 



