42 THE PROTOZOA 



suspended in the form of a network in another fluid with which it 

 does not mix a condition which could not exist for more than an 

 instant of time, since the fluid reticulum must break up immediately 

 into minute droplets. If, on the other hand, the reticulum is of 

 rigid consistence, the protoplasm as a whole could not be fluid, 

 any more than a sponge soaked in water could behave as a fluid 

 mass in the aggregate. The difficulty can, however, be overcome 

 by supposing the apparent reticulum to be the optical expression, 

 not of a fine network of fibrils, but of delicate lamellae limiting 

 minute closed chambers, or alveoli. Then the fine line seen with the 

 microscope joining any two adjacent nodal points would be the 

 optical section of the wall or lamella separating two contiguous 

 alveoli, and protoplasm as a whole would possess a honeycombed 

 structure comparable to that of a fine foam or lather the fluid 

 lamellae of the foam represented by the apparent reticulum of the 

 protoplasm, and the air-contents of the individual bubbles repre- 

 sented by the enchylema. Or, to express the state of things in a 

 different manner, protoplasm could be regarded as an emulsion of 

 very fine structure, composed of two fluids not miscible with one 

 another namely, the more fluid enchylema, which is suspended 

 in the form of minute droplets in the more viscid substance forming 

 the alveolar framework. This is the so-called alveolar theory, 

 especially connected with the name of Biitschli ; by this conception 

 of protoplasmic structure, not only are the necessary physical con- 

 ditions satisfied, but an explanation is given for many peculiarities 

 of protoplasmic bodies, such as the radiate arrangement of the 

 meshes of the reticulum commonly observed either at the surface of 

 the body or around solid or fluid bodies contained in the proto- 

 plasm, and so forth. 



The various theories that have been mentioned all assume tacitly 

 that protoplasm is monomorphic that is to say, that it possesses 

 one fundamental type of minute structure. Fischer, on the other 

 hand, seeks to unite all the different theories by supposing that 

 protoplasm is a polymorphic substance that is to say, one that 

 may exhibit a diversity of structure at different times and under 

 different conditions, as the result of changes produced by its inherent 

 vital activity. Thus, he supposes that a given mass of protoplasm 

 may be at one time .homogeneous, and at another time granular, 

 reticular, fibrillar, or alveolar, as the result of a process of " vital 

 precipitation," and that by reabsorption of the structural elements 

 it may return to a homogeneous condition. Faure-Fremiet (38 and 

 38'5) also regards protoplasm as a homogeneous fluid, which is pre- 

 cipitated by reagents, and which normally contains, in suspension, 

 a certain number of granulations, some temporary, others per- 

 manent in nature ; compare also Degen (154). 



