CELL-CONTENTS AND FORMS OF CELLS. 215 



of assimilation in the chloroplastid. The fact that fungi con- 

 tain it shows that lecithin may be formed from protoplasm itself. 

 It is one of the most interesting compounds which has been 

 isolated from plants, and no doubt plays an important role in 

 the life of the cell. 



Lecithin is a yellow, viscous, waxy substance soluble in oils 



FIG. 117. Phytosterol allowed to crystallize very slowly from strong alcoholic solu- 

 tions, the crystals being recrystallized until the melting-point is constant. I, crystal forms 

 with parallel extinction C D. II, crystals with parallel extinction B C. Ill, crystals with 

 parallel extinction along the long axis. IV, common crystal forms of phytosterol. Phytosterol 

 is a constituent of most vegetable oils and is most abundant in peas, lentils, and other 

 Leguminous seeds. The presence of vegetable oils is detected in animal oils by a study 

 of the forms of crystals, those of phytosterol crystallizing in the monoclinic system, whereas 

 cholesterol forms crystals which belong to the triclinic system. After A. Bomer, in Zei'/s. 

 /. Unter. d. Nahr.- u. Genussmittel, 1898, p. 45. 



and warm alcohol. In solutions of ether or chloroform it is pre- 

 cipitated upon the addition of acetone. In contact with water, it 

 separates in the form of spiral threads or loops, giving rise to the 

 " myelin forms " of Kirchow and Beneke. When examined 

 | under the microscope a smear of lecithin, to which a drop of 

 water or a sugar solution has been added, sends out a number of 



