202 PHYSIOLOGY CHAP. 



it was itself derived. Nageli gave the name of idioplasm to the 

 hereditary substance represented by the sexual pronuclei which 

 fuse together in the act of fertilisation ; the germ which results 

 from it contains the images of the two individuals from which it 

 arises, and is therefore capable of transmitting by heredity their 

 characters to the individual which develops from it. It is, more- 

 over, necessary to admit that the idioplasm is a kind of microcosm 

 from which will develop the macrocosm, resulting from a myriad 

 of particles, materially different, and disposed in a certain regular 

 order, bearers of hereditary characteristics and tendencies, and 

 endowed with peculiar and special energies. To these particles 

 different names were given by different authors ; as representing 

 the elementary components of idioplasm, we shall follow 

 0. Hertwig in calling them idioblasts. " As physics and chemistry 

 (wrote de Vries) go back to molecules and atoms, so the biological 

 sciences have for their objective these units (idiollasts'} in order to 

 explain from their combination, the phenomena of the world of 

 living beings." 



Nageli also thought that the anatomical structures and the 

 physiological functions, which we perceive in the adult organisms 

 in the most complex conditions, are reduced in the idioplasm to 

 their most simple elements (represented by the idioblasts). 



"With the insufficient scientific knowledge which we possess 

 to-day, we are not in a position to state or even to imagine in 

 what consists the specific nature of the different idioblasts ; how- 

 ever from the definition alone of biological units carrying heredi- 

 tary characters, we may draw some conclusions relative to their 

 more general properties. 



As we attribute to the cells, which are the elements of the 

 complex organisms, all the vital specific properties by which living 

 beings are distinguished from inorganic bodies ; so it is necessary 

 to attribute to the idioblasts, which are the essential elements of 

 the cells, all the vital properties by which the cells are differenti- 

 ated from organic substances without organisation. It is easily 

 understood that the idioblasts must grow and multiply by division 

 as do the cells. In fact, all the daughter cells proceeding from 

 the mother cell, represented by the fertilised ovum, must contain 

 special idioblasts arising from the ovum, without which the adult 

 organism could not repeat the characters of the parents, nor be 

 capable of forming in its turn the sexual cells which in their idio- 

 plasm contain the sum of the hereditary elements represented by 

 the idioblasts. It is then a strictly logical consequence that the 

 idioblasts of the ovum grow and multiply by division during the 

 development of the germ. Through their divisibility the idio- 

 blasts are clearly distinguished from the molecules of physics and 

 chemistry, which cannot divide without changing their nature 

 and characters. We must then imagine them as very complex 



