ITS CHEMICO-PHYSICAL AND MORPHOLOGICAL PROPERTIES 19 



examined ; in the latter, its most minute structure has been 

 rendered visible, by means of various staining reagents ; thus we 

 have ah-eady a considerable amount of literature on the subject 

 of the structure of protoplasm. 



Starting with the assumption that protoplasm consists of a 

 mixture of a small quantity of solid substances with a large 

 quantity of fluid, to which circumstance it owes its peculiar 

 viscid property as a whole, the question might be raised as to 

 whether it be possible, by using the strongest lenses, to distinguish 

 optically the solid particles from the fluid which contains them, 

 and to recognise their arrangement into special structures. A 

 priori, it does not seem to be necessary to distinguish them 

 from one another, since the solid particles are so very small, and 

 since they differ so little from the fluid in their refractive power. 

 Thus, according to Nageli's micellar theory, which will be de- 

 scribed in detail later on, they are supposed to be arranged as 

 a framework, which, hotvever, in consequence of the minute size of 

 the hypothetical micellse, escapes our observation. In a word, it is 

 possible that protoplasm may have a very complicated structure, 

 although it appears to us to be a homogeneous body. Hence the 

 expression homogeneous protoplasm does not necessarily imply that) 

 protoplasm does not possess a definite structure or organisation. } 



Recent observations, for which powerful oil immersion lenses 

 have been successfully used, point more and more to the conclusion 

 that protoplasm possesses a structure which may be optically 

 demonstrated ; however, individual microscopists differ so essen- 

 tially in their views upon the nature of this structure, that it is 

 impossible to come to any definite decision upon the subject. 



At the present time, at least four conflicting theories hold the 

 field ; these may be described as the framework theory, the foam 

 or honeycomb theory, the filament theory, and the granula theory. 



The framework theory has been advocated by Frommann (II. 14), 

 Heitzmann (II. 17), Klein (II. 21), Leydig (II. 26), Schmitz 

 (II. 30), and by others. According to this theory, protoplasm 

 consists of a very fine network of fibrilloe or threads, in the inter- 

 stices of which the fluid is held. Thus, roughly speaking, it is 

 like a sponge, or, shortly expressed, its structure is spongiose. 

 The microsomes, which are seen in the endoplasm (granular 

 plasma), are nothing but the points where the fi brill se intersect. 



A glance over the literature on this subject shows the reader 

 that very different appearances are sometimes described under the 



