Guilllerniond - Atkinson 



136 



Cytoplasm 



solution as in differentiated cells. Neutral red behaves differently 

 with the two types of vacuoles. 



In the small vacuoles of very concentrated colloidal contents, 

 neutral red does not cause any precipitation and stains deeply and 

 homogeneously. These small vacuoles are not usually visible with- 

 out the assistance of vital dyes. There are cases, however, in which 

 they appear very distinctly because of the anthocyanin (red or 

 violet) which they always contain and which gives them a natural 

 color. Such is the case in the vacuoles of teeth of young rose leaflets 

 (Fig. 92), which will be mentioned later. The study of these 

 vacuoles in the living state makes it possible to see that they have 

 exactly the same shape as those which are obtained by vital stains 

 in cases where the vacuoles are not otherwise visible. There are 

 cases in which the small vacuoles of meristematic cells, because of 



the high refractivity of their contents, 

 are perfectly visible without vital dyes 

 (barley root, wheat root, first leaves of 

 the bud in Iris germanica) . The stain- 

 ing of these small vacuoles with neu- 

 tral red may be followed under the 

 microscope and it may be observed 

 that this staining is not accom.panied 

 by any alteration — on condition, of 

 course, that the observation is not too 

 greatly prolonged, for at the end of a 

 certain time a swelling of the vacuoles 

 always occurs. 



The large vacuoles with very disperse 

 colloidal contents are, on the contrary, 

 always visible without staining and it 

 is very easy with the microscope to 

 follow the different phases of their 

 staining with vital dyes. The phenom- 

 ena are very clear cut, particularly in the fungi (molds and yeasts) . 

 For example, by placing cells of Saccharomy codes Ludwigii grown 

 in a van Tieghem and Le Monnier moist chamber (Fig. 88) in a 

 drop of neutral red solution, it is observed that there are immediate- 

 ly produced in the vacuoles, a great number of granules strongly 

 stained and showing Brownian movement. These are the result 

 of precipitation of the vacuolar colloid through the action of neu- 

 tral red. It sometimes happens that these precipitates, carried 

 against the wall of the vacuole, pass through it and are deposited 

 in the peri vacuolar cytoplasm (Fig. 86), a phenomenon which is 

 also caused by fixatives and which leads to errors of interpretation. 

 This precipitation occurs even if an extremely dilute solution of 

 neutral red is used. The reaction is, therefore, very delicate and 

 the vacuolar colloid is very readily stained by the dye, but if the 

 solution is very dilute, the phenomenon stops with the production 

 in the vacuoles of small colored granules, showing Brownian 

 movement. If, on the contrary, the solution is more concentrated, 



Fig. 87. — ■ Saccharomycodes Lud- 

 wigii. Vital staining. Neutral red 

 produces small precipitates in the 

 vacuole, showing Brownian move- 

 ment (o) which then fuse to form 

 larger bodies (o') sticking to the 

 periphery of the vacuole (a") and 

 then dissolve, leaving the vacuole 

 dififusely stained {a'"). B, similar 

 series. 



