14 ANDREWS. 



tricably mingled ; yet for the physicist they remain clearly dis- 

 tinguishable at any given moment. 



That this is true for the physiologist also will be presently 

 shown. 



DISCONTINUOUS ELEMENTS OR INCLUSIONS. 



In character these are most heterogeneous. They may be 

 subdivided into Simple and Compound inclusions. They are 

 fluids, of various degrees of viscidity, with or without suspended 

 substances^; or solids ; they may be concretions, or secretions, 

 or excretions ; native or adventitious. 



Even very small areas are found to contain many chemically 

 different inclusions. 



Under Simple Inclusions are grouped the alveolar contents 

 of Butschli's structure, or of the finer froth, or of coarser alveo- 

 lation; wherever no interpenetration of the continuous element, 

 subdividing the mass into a finer froth can directly or indirectly 

 be detected. Simple inclusions may be of one substance, or of 

 a number of mechanically mingled substances. They are some- 

 times transformed into members of the second group by activi- 

 ties of the lamellar substance.^ 



Under the head of Compound Inclusions are placed those 

 areas, irrespective of both actual and relative size, where are 

 grouped together alveoli, containing, as far as can be optically 

 or chemically demonstrated, the same, or very similar, discon- 

 tinuous substances. 



The lamellar substance of these inclusions unites to form one 

 common pellicle which, with or without modification of various 

 sorts, separates them as a mass from adjacent protoplasm. 

 Such groups may be built up on a basis of the finer froth; and 

 then form one or more inclusions of Butschli's structure ; or 

 they may be built up of the latter only, or of both ; but in all 

 cases the mass is an aggregate of single vesicles, and therefore 

 interpenetrated at some time, if not always, by the continuous 

 substance, which when visible forms an optical network. 



^ The Protozoa furnish endless instances of mingled inclusions. 

 2 See p. 19. 



