THE CELL 277 



In order to grasp these figures F. HOFMEISTER shows how a struc- 

 ture might be erected whose molecules are bricks, not to exceed in 

 number 200,000 milliards, of which 200 milliards colloid molecules 

 with a portion of the salt molecules form the walls, roof, ceilings, 

 etc., whereas the water molecules with the remaining crystalloid 

 molecules fill the rooms, halls and corridors. If such a structure had 

 the enormous average height of 50 meters it would cover a ground 

 space 7000 square kilometers or one-half the area of Alsace-Lorraine. 

 It is evident that the compexity of the molecular structure of a cell 

 baffles our powers of description. 



A cube with edges 0.1/x which is much smaller than the limits of 

 microscopic visibility contains 25 million molecules of water, 25 

 thousand molecules of colloidal, and 250 thousand molecules of 

 crystalloidal substance, which under the same conditions would cor- 

 respond to a building 100 meters front, 20 meters high and 20 meters 

 deep. 



Protoplasm. 



Until recently there was little definite knowledge concerning the 

 colloidal nature of protoplasm, that is, whether it was fluid or gela- 

 tinized. It was known that after the fragmentation of yeast cells it 

 was possible to press out a juice containing various enzymes, and 

 that meat juice obtained in a similar manner contained albumin. 

 In the case of yeast it may be inferred that the protoplasm contains 

 sols, but in the case of muscle such an inference is met by the objec- 

 tion that the albuminous substance may have arisen from the blood 

 serum which bathes the muscle fibers. The facts that portions of 

 cells form drops and that foreign fluids in protoplasm assume spherical 

 shapes likewise point to the fluid nature of many protoplasms. 



Most of the numerous investigations concerning the physical 

 nature of protoplasm are at present of mere historical interest, 

 since the ultramicroscope has solved many of the main questions or 

 has placed us in a position to do so in the future. One of the most 

 important criteria for differentiating between a sol and a gel l is the 

 presence of Brownian movement. If it is possible to observe an 

 oscillatory movement in the granules of a cell, such granules must 

 be in a fluid medium; if they are motionless the medium must be 

 either a gel or very viscous. If we observe that the oscillating 

 movement has ceased, it means that the fluid has gelatinized. 



Numerous ultramicroscopic observations of cells have been pub- 

 lished. Plant cells have been studied most carefully by N. GAID- 

 UKOV.* He studied the pollen hairs of tradescantia, myxomycetes 

 (slime fungi), the cells of various algae (spirogyra, cladophora, cedogo- 



1 [There is no sharp line between sol and gel. The more viscous the medium 

 the longer time the changes take, ric^ metals for examples. Tr.] 



