362 THE POPULAR SCIENCE MONTHLY. 



structure and perturbations of function to which living matter is 

 liable; and, secondarily, medicine deals with the applications of the 

 knowledge thus acquired for the checking of these perturbations and 

 the renewal of normal structures in other words, for the relief of 

 suffering and the restoration and preservation of health. 



The Held of medicine is, then, a large one. As already intimated, 

 some knowledge of the various natural sciences is essential to its suc- 

 cessful study ; not only by reason of the fact that living matter is sub- 

 ject to the same chemical and physical laws as non-living matter, but 

 also because of the intimacy of its relations to its physical environ- 

 ment, and of the constancy of the reactions between every organism 

 and its environment. 



As a general introduction to the course of medical study now 

 opened in this college, it has therefore seemed appropriate to devote 

 an hour to a brief biography of Protoplasm, the universal life-substance 

 from which all organisms, whether vegetable or animal, originate, and 

 modifications of which constitute even the most complex tissues of the 

 highest animal forms. 



Though so universally diffused, though the autobiography of pro- 

 toplasm has been written in the life of every plant and animal since 

 creation's dawn, it is still a hidden story in some of its earlier chapters. 

 Perhaps it is the very simplicity of its origin that balks us: we would 

 fain invoke some supernatural explanation of the growth-force and 

 the capacity for development which belong to this substance, as dis- 

 tinct from non-living matter, forgetting that all natural forces are 

 equally elusive and obscure. Why do certain kinds of matter always 

 crystallize in certain fixed and characteristic forms? Why, on the 

 other hand, is protoplasm formless, but capable of endless develop- 

 ment and change ? 



There are certain chemical and physical differences between crys- 

 tallizable and non-crystallizable substances which, if fully understood, 

 would no doubt furnish an answer to this question. 



Protoplasm, a non-crystallizable substance, is both physically and 

 chemically of a highly complex composition not determined with ex- 

 actness, but known to consist mainly of hydrogen, oxygen, nitrogen, 

 and carbon, variously combined in such proportions as to produce 

 representatives of three classes of chemical substances the albumi- 

 noids, the starches, and the fats the albuminous constituents largely 

 predominating in native undifferentiated protoplasm. 



With these compounds is associated a considerable though varying 

 proportion of water, as well as smaller quantities of saline and other 

 crystalline substances. 



Of the molecular structure of living, active protoplasm, nothing 

 definite is known ; it is, however, probable that the albuminoid matter 

 of its massive molecule is associated with a complex fat and with some 

 form of starch ; while the water and the salts may be loosely combined 



