498 EDWARD B. MEIGS 



INTRODUCTION: THE PRESENT STATE OF THE SUBJECT 



The work, of which this article gives the results, has been 

 directed toward throwing light on two main questions. The first 

 of these may be roughly described as that of the ' osmotic proper- 

 ties' of vertebrate smooth muscle. WTiat are the results of sub- 

 jecting smooth muscle to such experiments as are thought to 

 demonstrate that the fibers of striated muscle are surrounded by 

 semi-permeable membranes; and what are the physical conditions 

 of the water, colloids, and crystalloids of the smooth muscle fibers? 

 The second question is that of the chemical and physical processes 

 which bring about contraction in smooth muscle. The close rela- 

 tion between these two questions will become apparent as the 

 article progresses. 



The investigations of the last fifty years have shown very 

 clearly that the behavior of a tissue which is removed from the 

 body and immersed in a foreign medium is often highly dependent 

 on the osmotic pressure of that medium. It is a general rule that 

 tissues remain longest in a state approaching the normal in those 

 media which have about the same osmotic pressure as the blood 

 plasma and lymph of the animal from which they were taken; 

 they tend to give up fluid to hypertonic solutions and to take fluid 

 from hypotonic solutions.' These facts have given rise to the 

 view that the cells of animal tissues are surrounded by semi- 

 permeable membranes and a great deal of work has been directed 

 toward discovering the exact nature of these membranes. 



Recently, however, the behavior of such colloids as gelatin and 

 fibrin in various electrolytic and non-electrolytic solutions has 

 received careful attention. It has been shown that these colloids 

 have a remarkable tendency to take up water from certain solu- 

 tions, and that the strength of this tendency depends in a compli- 

 cated manner on the nature and concentration of the electrolytes 

 present. It has been pointed out that the behavior of muscle 

 under many conditions resembles that of gelatin and fibrin, and 

 this resemblance has led certain investigators to deny the exist- 



^ The word 'hypertonic' is used throughout this article to mean that a solution 

 has a higher osmotic pressure than the blood plasma of the animal under discus- 

 sion; the word 'hypotonic,' to mean that the solution has a lower osmotic pressure 

 than the blood plasma. 



