154 THE PATH OF SCIENCE 



Scottish botanist Robert Brown (as eminent in plant geog- 

 raphy as in microscopical studies) recognized the nucleus as 

 a regular feature in plant cells. It had already been named in 

 1823, but the universality of its occurrence had never been 

 realized. Attention had been focused on the cell wall, a mere 

 lifeless box, and not on the living substance within. The 

 most obvious object in the living substance within the box 

 is the spherical or oval nucleus, and it is perhaps not strange 

 that the nucleus attracted attention before the substance in 

 which it was embedded. Now at last the substance itself was 

 studied, by the French zoologist Felix Dujardin, who called 

 it sarcode. His description of it was remarkably accurate. 

 "I propose to give this name," he wrote, "to what others have 

 called a living jelly— this viscous, transparent substance, in- 

 soluble in water, contracting into globular masses, attaching 

 itself to dissecting needles and allowing itself to be drawn out 

 like mucus; occurring in all the lower animals interposed be- 

 tween the other elements of structure." We could hardly do 

 better today in so few words, though nowadays we have nu- 

 merical data for viscosity and elasticity, and we should not 

 restrict the substance to the lower animals. Dujardin's word, 

 however, did not stick. The Czech investigator Johannes 

 Purkinje introduced protoplasm, and this caught on some 

 years afterward when the great cytologist Hugo von Mohl of 

 Tubingen applied it to the same substance in plants. 



Purkinje did something a good deal more important than 

 introduce a useful new word. He pointed out that the skin 

 of animals, especially embryos, consists of cellulae like those 

 forming the connective substance or parenchyma of plants. 

 The stage was now set for the enunciation of the cell theory. 



It was in October 1838 that the ex-lawyer M. J. Schleiden 

 and the anatomist Theodor Schwann dined together in 

 Berlin. They were a strangely assorted pair. The volatile 

 Schleiden, having shot himself in the forehead and recovered, 

 can have had little in common with the placid Schwann apart 

 from their intense interest in the minute anatomy of organ- 



