THE LIVING SUBSTANCE. 1 3 



Other forms of the Protozoa which crossed the path of my work 

 from time to time, and were used passingly as corroborative 

 evidence ; Hydra viridis and Hydra fusca ; Turbellarians ; An- 

 guillulidae ; Rotiferae, adult and embryo ; Starfish and Echinus 

 embryos and larvae ; frogs' eggs ; fish eggs ; tadpole's "tissues ; 

 crabs' tissues and the Leucocytes of crabs' blood ; also many 

 fresh-water Crustacea ; fresh sciatic muscle of the dog. In 

 plants, Spirogyra, Chara, Nitella. 



Composition of the Protoplasmic Foam. 



The protoplasmic froth is infinitely complex in character of its 

 constituents, and in arrangement and grouping of these, which, 

 in Metazoa as well as in Protozoa, are subject to more or less 

 gradual change of size, and of actual, as well as relative, posi- 

 tion. 



[11] A substance formulated as a visco-fluid foam must have 

 its elements, however multiple their character, divided at any 

 given moment into two broad physical groups. This is the 

 state of things we find characterizing protoplasm. 



There is first the element, be its nature simple or complex, 

 which forms at any given moment the lamellar, or enclosing 

 substance, of the foam vesicles, throughout the whole or any 

 part of the series of structural subdivisions. 



This is, physically, the Continuous Substance. 



Secondly, we have those elements seen as the substances in- 

 cluded in the vacuoles, or cavities, of the foam : these are isolated 

 to some extent from each other by lamellar films ; and in each 

 structural series by interalveolar material, which in different 

 masses or areas, or in the same areas from moment to moment, 

 varies in thickness, in constitution, and structure, as well as in 

 quality, or viscidity. 



The substances so isolated are, therefore, at any given moment 

 the Inclusions, or the Discontinuous Substances. 



Where the continuous, or interalveolar substance, is itself a 

 compound emulsive froth, repeating the characters of the whole 

 mass, it is true the two groups of elements, from the standpoint 

 of Biitschli's structure, may seem to be in a sense almost inex- 



