118 LECTURE VI. 



or that cholesterol is present in a different form, or perhaps to a different 

 extent in one case than in the other. Perhaps when the cholesterol is in a 

 combined state lecithin may act normally; and conversely, lecithin may 

 be in some such state of combination that it is less active, so that in the 

 different processes of the cell at one time lecithin acts freely, while at 

 another it does not. 



The terpenes, and especially the cyclic terpenes, are very widely dis- 

 tributed in the vegetable kingdom. Plant secretions are largely composed 

 of these. We are acquainted with a large number of the members of this 

 class. Limonene and pinene are most widely distributed. At present we 

 cannot say anything 1 regarding their functions or their origin. 



1 Cf. F. Czapek: Biochemie der Pflanzen, G. Fischer, Jena, 1905, vol. ii, p. 658 



