CELL-CONTENTS AND FORMS OF CELLS. 



21 



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 r(Me in 

 the life of the cell. 



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



/N 



A 



W 



9 



hy 



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 Zeits. 

 f. 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 



