84 THE CELL DOCTRINE. 



given by Schleiden, are by no means constant, it is 

 plain tbat wbat is commonly known as tbe nucleolus 

 is here intended, to tbe discovery of which we are 

 therefore indebted to him, though Valentin also 

 claims its discovery at an earlier period.* He fur- 

 ther states that the observations he has made upon 

 all plants, lead him to the conclusion that these small 

 bodies are found earlier than the cytoblasts. 



According to Schleiden, when starch, which is 

 superfluous nutritive material deposited for future 

 use, is to be employed in new formations, it becomes 

 dissolved into sugar or gum, which are convertible 

 into one another. The sugar appears as a perfectly 

 transparent fluid, not rendered turbid by alcohol, 

 and receiving from tincture of iodine only so much 

 color as corresponds to the strength of the solution. 

 The gum is somewhat yellowish, more consistent, 

 less transparent, and coagulated into granules by 

 tincture of iodine, assuming a pale yellow color, 

 which is permanent. In further progress of organi- 

 zation, in which the gum is always the last inmiedi- 

 ately preceding fluid, a quantity of exceedingly mi- 

 nute granules appears in it, most of which, from 

 their exceeding minuteness, appearing as black points. 

 It is in this mass that organization takes place, 

 though the youngest structures are composed of 

 another distinct, homogeneous, perfectly transparent 

 substance — so transparent as to be invisible when 



* Valentin, "Outline of the Development of Animal Tissues,'' 

 in Wagner's Elements of Physiology, translated by Dr. Willii". 

 London, 1844, p. 214; Leipzig, 1839 ; where he refers to Valen- 

 tin's Eepertorium, vol. i, p. 143. 



