Chapter I — 3 — Introduction 



ticular, of the chromosomes, whose form in the fixed material is 

 preserved with a minimum of distortion. 



On the other hand, as far as the cytoplasm is concerned, the 

 paraffin method has, over an extremely long period, given only 

 mediocre results and cytologists have made the mistake of neglect- 

 ing too greatly the study of living material. As a matter of fact, 

 the most convincing data on the cytoplasm were for a long time 

 obtained exclusively from living cells: on the one hand, the 

 excellent discoveries of SCHMITZ concerning the chloroplasts 

 of the algae and those of WiLHELM ScHiMPER and Arthur Mayer 

 in the study of plastids of higher plants, and, on the other hand, 

 the classical experiments of Hugo de Vries on the vacuoles and 

 their role in the osmotic phenomena of the cell. 



It is only since 1910 that knowledge of the cytoplasm has made 

 rapid progress. At that date, the timely appearance of the ultra- 

 microscope enabled A. Mayer and Schaeffer to make known some 

 essential data on the colloidal nature of the cytoplasm of animal 

 cells — data which can be applied to plant cells. At about the same 

 time, the introduction of mitochondrial viethods, new fixation tech- 

 niques for certain cytoplasmic lipides, led to the discovery of the 

 chondriosomes and made it possible to preserve the plastids, to 

 stain them clearly and to follow them through their whole life 

 history. A little later, the methodical use of vital dyes, which 

 accumulate in the vacuoles of living cells, made it possible to follow 

 the evolution of the vacuoles through all the stages of cellular 

 development. Finally, the invention of the micromanipulator and 

 of motion-picture photography, and the perfecting of methods of 

 observation in vivo, have contributed in large part to making 

 known to us the physical properties of the cytoplasm and of its 

 various morphological elements. 



Difficulties in the study of cytoplasm. Recommended method :- 



As a result of work carried on during the last twenty years by 

 means of the mitochondrial technique, or with the aid of the ultra- 

 microscope, or by the use of vital dyes, it has been possible to solve 

 definitely the problem of cytoplasmic structure. The discoveries in 

 this domain are still too recent to be accepted by all cytologists. 

 But if these are still being discussed, it is simply because they have 

 been arrived at by methods very different from those usually em- 

 ployed and because some cytologists are unable to verify them by 

 their own methods. The study of the cytoplasm, a substance which 

 is very easily injured, is infinitely more difficult than the study of 

 the nucleus. It is necessary to use a long and delicate method 

 whose general outline will be indicated here. 



This method, which will be called the analytical method, i.e., 

 analysis of the cell, consists of the following serial operations: 

 First, this method requires the use of fixed and stained sections 

 which are indispensable in bringing out the elements which are 

 considered as entering into the constitution of the cytoplasm. But 

 this method is always insufficient, for once these elements have been 



