THE LAWS OF LIVING PROTOPLASM 17 



constantly in mind Lord Kelvin's generalizations 

 of some fifty years ago, "Dead matter cannot be- 

 come living without coming under the influence 

 of matter previously living." 



Closely associated with the chemical properties 

 of protoplasm are its physical properties which are 

 obvious to even a casual student. But there still 

 remains so much to be discovered in regard to the 

 physical nature of living substance that we are not 

 justified in regarding the conclusions as entitled to 

 rank as a law, so they must be stated as theories. 



The Physical Properties of Protoplasm. — 

 When protoplasm is studied by means of the 

 microscope, it presents a certain appearance. This 

 varies with the kind of protoplasm being studied 

 and whether it is alive or has been fixed by such 

 chemical agents as picric acid, formalin, etc. Up 

 to the present it has been impossible to give a 

 single, physical description of protoplasm that 

 applies to plant and animal, muscle and nerve, or 

 egg and gland cell protoplasm. The physical pic- 

 ture presented by protoplasm under different con- 

 ditions of activity and in different organisms has 

 been accounted for by the two following theories, 

 neither of which is entitled to be ranked as a law. 



a. Fibrillar Theory. — The adherents to this 

 theory claim that a distinct meshwork of cyto- 

 plasmic fibrils can be made out when suitable 

 treatment is employed and such terms as 



