STRUCTURAL BASIS OF PROTOPLASM 19 



blance to actual protoplasm, and that drops of oil-emulsions suspended 

 in water may even exhibit amoeboid changes of form. 



Opposed to Biitschli's conception is the view, first clearly set forth 

 by Frommann and Arnold ('65-'6/), and now maintained by such 

 authorities as Flernming, Van Beneden, Strasburger, and perhaps the 

 greater number of contemporary investigators, that the more solid 

 portion consists of coherent threads which extend through the ground- 

 substance, either separately or connected by branches to form a mesh- 

 work like the fibres of a sponge (Figs. 7, 9). 



In the present state of the subject it is difficult, indeed, impossible, 

 to decide which of these opposing views should be accepted ; for the 

 evidence is very strong that each expresses a part of the truth. It is 

 generally admitted that such an alveolar structure as Biitschli de- 

 scribes is characteristic of many unicellular forms, and occurs in 

 many higher forms where the cell-substance is filled with vacuoles or 

 with solid inclusions such as starch-grains or deutoplasm-spheres. 

 In the latter case the structure has been termed "pseudo-alveolar" 

 (Reinke); but it remains to be seen whether there is any real dis- 

 tinction between this and the true alveolar structure described by 

 Biitschli. On the other hand the evidence of true fibrillar or reticular 

 structure in many tissue-cells, especially during cell-division, is very 

 convincing; and my own observations have led me to regard this 

 structure as the more typical and characteristic. For descriptive pur- 

 poses I shall accordingly adopt the terms of the fibrillar or reticular 

 hypothesis, designating the more solid portion of protoplasm as the 

 thread-work or reticulum. ("Geriistwerk," " Fadenwerk " of German 

 writers) in contradistinction to the more liquid ground-substance. It 

 should be clearly understood, however, that these terms are used only 

 as a matter of convenience, and are not meant to exclude the possibility 

 that the ''fibres" or the "reticulum" may in many cases be open to 

 Biitschli's interpretation. 



From a theoretical point of view the finer structure of the network 

 is a question of very great interest ajid importance. The earlier 

 investigators, such as Virchow and Max Schultze, failed to observe 

 the thread-work, and described protoplasm as consisting of a clear 

 homogeneous basis in which were embedded numerous granules. 

 Even at the present time a similar view is held by a few investi- 

 gators, more especially among botanists (e.g., Berthold, Schwarz), 

 who regard the thread-work either as an artificial effect produced 

 by reagents, or, if normal, as an inconstant and hence unimportant 

 feature. The best and most careful recent studies on proto- 

 plasm have, however, yielded very convincing evidence that, what- 

 ever be the precise configuration of the protoplasmic reticulum, 

 it is not only a normal structure, but one of very wide occurrence. 



