44 PROTOPLASM 



The sudden changes in protoplasmic consistency, from quite 

 liquid to very firm, have been compared to the thixotropic 

 behavior of gels (page 150). While no specially constructed 

 model is here necessary, yet any gel which also goes through 

 these changes becomes for the moment a model. 



Freundlich has observed spindle-shaped figures in concentrated 

 vanadium pentoxide and benzopurpurin which he believes may 

 be formed in a manner similar to the spindle of a dividing cell 

 (page 20). The former when made to reproduce the latter is a 



model of it. 



A number of the properties of protoplasm, such as its elas- 

 ticity, may be duplicated in nonliving matter, particularly gels, 

 which thus become models of the living substance in so far as 

 they imitate one quality. 



Imitations of living cells as a whole have often been attempted. 

 Among the first of these were the experiments of Berthold, 

 in imitation of the movements of amoebae. The experiments of 

 the Mexican Herrera include imitations of many cellular activ- 

 ities. By placing drops of caustic soda stained with rhodamine 

 in a mixture of 1 part olive oil, 1 part resin, and 40 parts gasoline, 

 Herrera produced what he called "colpoids," which are imitation 

 amoebae. They show internal flow as well as body movements, 

 due to changes in surface tension and the repulsive action of 

 osmotic currents. A number of other reactions occur in these 

 colpoids in imitation of vital processes, such as conjugation (the 

 fusion of two individuals), deformation, contraction of vacuoles, 

 formation of pseudopodia, division, growth, and the phagocytosis, 

 or ingestion, of carbon particles impregnated with acetic acid. 

 This last reaction is in imitation of the taking in of food by 

 Amoeba. A more familiar experiment of this kind is that of 

 Rhumbler, who showed that a drop of chloroform under water 

 will not take in a piece of glass, but if the glass is coated with 

 shellac it is immediately taken in. After "digesting " (dissolving 

 off) the shellac, the chloroform ejects the glass. A living amoeba 

 will ingest particles which are not good as food — particles such 

 as those of the dye carmine — and immediately give them up. 

 The three phenomena, a living amoeba eating real food (organic 

 matter), a living amoeba eating imitation food (carmine), and 

 an imitation amoeba (colpoid) "eating" imitation food (carbon) 

 may all be due to the same force, viz., a change in surface tension. 



