12 



SCIENCE. 



[N. S. Vol. XX. No. 496. 



body are more or less surrounded by the 

 blood and necessarily in equilibrium with 

 it. Any great variation in the osmotic 

 pressure of the blood would, therefore, be 

 followed by a change in the content or con- 

 centration of every dependent cell. It ap- 

 pears to be a special function of the kidney, 

 therefore, to eliminate just enough of the 

 accumulated blood products to keep this 

 mean osmotic pressure at its normal value. 

 If in any given case a wide divergence from 

 this is found by experiment, the conclusion 

 is at once drawn that some serious impair- 

 ment of the kidney has taken place. The 

 test is easily made with a small amount of 

 the blood by what is known as the cryo- 

 scopic method. Its diagnostic value is gen- 

 erally recognized. 



Similarly, we have in the determination 

 of electrical conductivity another simple 

 method of finding a certain kind of solu- 

 tion content. This method may be ap- 

 plied to body fluids, especially to the urine 

 and to the blood, and the informatic^n se- 

 cured has often considerable value, since it 

 is not exactly the same as may be obtained 

 by the methods of chemical analysis. The 

 general procedure has been applied in other 

 kinds of work, twenty years or more, but 

 only within the last four or five years have 

 the applications in medicine been thought 

 of. It will be recognized that these appli- 

 cations are comparable to new methods of 

 analysis and their value must be measured 

 from that standpoint. 



But the chief value of physical chemistry 

 to medicine does not lie in this direction, 

 practical as it may appear. The develop- 

 ment of the modern theory of solutions has 

 wrought a most wonderful change in our 

 mode of thinking of chemical problems, and 

 while for a time this change was noticeable 

 mainly in the treatment of questions of 

 inorganic chemistry, it has finally appeared 

 in the discussion of medical problems also. 

 In pharmacology the conception of inde- 



pendent ions is a helpful one in explaining 

 many points in the action of drugs which 

 have hitherto been obscure. It is well 

 known that the chemical activity of many 

 substances in solution may be greatly modi- 

 fied by the presence of other substances 

 having like ions free. Physiological ac- 

 tivity, it is found, is often modified in the 

 same manner, and beyond question the prob- 

 lem here presented will be found a fruitful 

 one in the theory of medication and in the 

 explanation of incompatibles. The im- 

 portance of certain ions in the blood and in 

 the muscular juices has just begun to be 

 clearly recognized and the maintenance of 

 these in right amount, even when only 

 traces may be present, is a chemical neces- 

 sity. It is known that the inorganic sub- 

 stances which yield ions have a necessary 

 duty to perform in the body. The con- 

 stancy of the one per cent, of mineral sub- 

 stances in the blood is doubtless more neces- 

 sary than the constancy of the twenty per 

 cent., or more, of organic substances. 



The physical chemists have given us a 

 number of new general methods of attack- 

 ing old problems. Some of them have an 

 important bearing on live questions in 

 medicine. For example, take the question 

 of the solubility of uric acid and the urates, 

 the deposition of which in the tissues is 

 supposed to be the source of many disor- 

 ders. For fifty years or more much has 

 been written on the problem of dissolving 

 these urate deposits or concretions, or of 

 preventing their formation. Lately several 

 writers have begun to study this .ever- in- 

 teresting topic from the standpoint of the 

 mass action law and dissociation hypothesis, 

 and in a way which promises much for the 

 clearing up of the fundamental conditions 

 • of deposition. It has already been pretty 

 well shown why certain suggested remedies 

 have not been of value and can not possibly 

 do what was long claimed for them. In the 

 uric acid problem two fundamental ques- 



