536 THE HISTORY OF BIOLOGY 



It was he who ascertained after detailed study the process of nuclear 

 division and actually gave to its various phenomena the names that have 

 been in use since then; owing to its strong colourability he called the fila- 

 ment substance "chromatin" and non-colourable substance, which also ap- 

 pears upon division, "achromatin"; the names of the different phases of 

 division — spirem, aster, metakinesis, dyaster, and dispirem — were also 

 invented by him. He also proved the conversion of the chromatin from a 

 network into a convoluted filament and further into a number of bent staves, 

 and proved that the actual division consists in these latter's splitting along 

 their length. These chromatin staves were afterwards called by Waldeyer 

 "chromosomes" and have, as is well known, come to play a decisive part 

 in modern heredity-research. The processes of the fusiform achromatin fila- 

 ments during division were also studied by Flemming; it was not until later 

 that the minute central body, the centrosome, which is of such vital impor- 

 tance for their transformation, was investigated, primarily by Flemming and 

 Boveri, who together with van Beneden discovered its division in cell- 

 reproduction. Boveri's studies of the centrosomes especially were very in- 

 tensive and have proved to be of fundamental importance. This formation 

 has been characterized by him as the cell's dynamic centre, which facilitates 

 the nuclear and cellular division. He also discovered that the centre of the 

 spermatozoon is formed thereby. 



While the nucleus has been found in the difi'erent forms of life to repre- 

 sent the conservative element — the chromosomes are, as is well known, 

 equally numerous and similarly formed in all cells in the same individual — 

 the protoplasm of the cell and its many and various derivatives have ofi'ered 

 fresh problems, owing to their wealth of form, which has proved all the 

 greater, the more these formations have been investigated. The actual basic 

 substance, which still has to bear the clumsy and illogical name of pro- 

 toplasm, has been investigated by a vast number of students and has called 

 forth many attempts at an interpretation of its essence. These attempts have 

 for the most part concentrated upon three diff"erent theories based on obser- 

 vation, which have been named after their founders: Biitschli's froth theory, 

 Flemming's filament theory, and Altmann's granule theory; to say nothing 

 of the purely speculative attempts to discover the fundamental substance of 

 life. The chief difficulty that revealed itself in these explanations and that 

 brought out their mutual contradictions is actually caused by the incon- 

 stancy which the living protoplasm always displays and which is a neces- 

 sary consequence of its role as bearer of all the metabolism in the cells and 

 the organisms composed of them. Even the nucleus displays phenomena of 

 substance-renewal and it has been found that the vital manifestations of 

 the cell ultimately receive their impulses from that quarter, but it is in any 

 case in the plasma substance that these manifestations of life are essentially 



