Chapter XIII 



— 131 



Vital Staining 



plants, the characteristic properties of metachromatin, with which 

 they have in common only the ability of forming absorption com- 

 plexes with vital dyes. 



It is well established, therefore, that the affinity of the vacuoles 

 for vital dyes, with some exceptions which will be taken up 

 later, is a general property of vacuoles and that this is due, 

 not to the presence in the vacuoles of a specific substance cor- 

 responding to metachromatin, but to colloidal substances whose 

 nature may vary radically, depending on the species in question. 



The presence of colloids in the vacuoles has, moreover, been 

 confirmed by another method. This has been employed by Weber, 

 Frey, and Reilhes, who tried to determine the degree of viscosity 

 of the vacuolar sap by observing the rapidity with which certain 

 solid bodies (calcium oxalate or calcium sulphate crystals, lipide 

 concretions) contained in the vacuoles fall 

 in their liquid when the microscope is in- 

 clined. Frey was able to show by this meth- 

 od that the viscosity of vacuolar sap of Clos- 

 terium cells at 18° C. is about twice as great 

 as that of water. This viscosity increases 

 considerably in dead cells. After cells have 

 been fixed, it becomes impossible to obtain a 

 fall of the calcium oxalate crystals contained 

 within their vacuoles. This can be explained 

 only by the fact that they are surrounded 

 within the vacuoles by coagulated colloids 

 which prevent them from moving. 



Finally, the more recent research of 

 Weber on "vacuolar contraction," which 

 will be taken up later, brought forward 

 new data in favor of the presence in the 

 vacuoles of colloidal substances which may 

 be true gels. 



Fig. 84. — Zea Mays. 

 Living cell stained with 

 neutral red, from the 

 aleurone layer at the be- 

 ginning of germination of 

 the seed; aleurone grains 

 have become diffusely stain- 

 ing vacuoles containing one 

 or more deeply stained 

 protein bodies (P) and one 

 or more colorless globoids 

 (G). 



Action of vital dyes on the cells. Advantages of vital staining :- 



When colloidal substances endowed with an affinity for vital dyes 

 had been demonstrated to be generally present in vacuoles, there 

 remained the task of determining more specifically the action of 

 these dyes on the cells. Do they accumulate exclusively in the 

 vacuoles or may they stain at the same time other cytoplasmic in- 

 clusions? Have they an injurious action on the cells and are they 

 not capable of altering the shape of the vacuoles? Or may they 

 not even bring about the appearance of artificial vacuoles in the 

 cytoplasm? These are questions which were raised. It was all 

 the more important to elucidate them since the vacuoles of em- 

 bryonic cells appear as minute elements with very concentrated 

 colloidal contents which usually can be revealed only by the use 

 of vital stains. Very accurate work carried out recently on vital 

 staining — our own work carried out over a period of twenty years 

 and especially our recent work in collaboration with Gautheret — 



