THE FROG : HISTOLOGY, GERM CELLS, DEATH 85 



more fluid hyaloplasm in its interstices. 1 Both these 

 substances are liquids containing various substances in 

 solution and others in suspension as granules and droplets. 

 Of the chemical composition of these solutions only the 

 broad outlines are known, since it is not possible to 

 analyse protoplasm without killing it and thereby bringing 

 about in it chemical changes. The solvent is water, and 

 in dead protoplasm the dissolved substances are in part 

 inorganic salts, such as the phosphates and chlorides 

 of sodium, potassium, and calcium, but principally 

 organic compounds, and those mainly colloidal. Some 

 of the organic bodies, such as glycogen and organic 

 compounds of ammonia, are comparatively simple and 

 were probably in course of assimilation or excretion by 

 the living substance, but the greater part are proteins, 

 which are peculiar to protoplasm and never found 

 except in it or in substances manufactured by it. 2 

 Metabolism never occurs without proteins, and its peculiar 

 features certainly depend largely upon the nature of 

 these substances, but it must not be overlooked that 

 metabolism is exhibited only when the proteins form 

 part of protoplasm, and only during the life of the latter. 

 The granules and droplets suspended in protoplasm vary 

 in composition and function. Some of them are truly 

 alive. They are probably of the same nature as the 

 spongioplasm but denser. Others, which may consist of 

 proteins, carbohydrates, or fats, are to be regarded as 

 material removed, for a time at least, from metabolism. 

 Among the most important of them are certain granules 

 which are revealed in the substance 3 of the meshwork 



1 This appearance is interpreted in various ways. It is probably 

 due, at least in some cases, to the fact that such protoplasm is a 

 foam or emulsion, the walls of whose bubbles are formed by the 

 spongioplasm while the hyaloplasm fills them. These minute bubbles 

 must not be confused with the larger spaces known as vacuoles. 

 The spongioplasm may contain threads of a substance still denser 

 than the rest of it, lying in the walls of the bubbles, and some 

 theories suppose that the whole of it has the form of threads. 



2 It is probable that during life the composition of protoplasm 

 is much more complex than that which we have outlined, and that 

 many of the bodies which can be obtained from dead protoplasm 

 are in life united in loose compounds. 



3 Known as linin. 



