12 THE NUTRITIVE PROCESSES 



liquid as a nutrient medium for the growth of Saccharomyces 

 depends much on the amount of resolution in this direction 

 which the organic compounds have undergone. 



To come to the second point : how the nutrient material 

 enters the organism. It has been suggested that the cell-wall may 

 consist of layers of molecules, in which the individual molecules 

 are so joined together as to constitute a membrane infinitely full 

 of interstices due to the inexact adaptation of the constituent 

 parts to each other, and that a series of layers, such as would con- 

 stitute the cell-wall, would form a more or less spongy envelope 

 permeable by substances whose molecular constitution was suffi- 

 ciently minute. The writer is not disposed to argue the tenability 

 of such an hypothesis, but the examination of numerous cells in 

 process of budding, under high magnifying power, has shown 

 that the manner of this production of the buds from the parent 

 cell is not incompatible with such a theory. 



To facilitate these examinations, various efforts were made to 

 stain the cells m such a way as to differentiate the layers of cell- 

 wall and the cell-contents without inducing, at the same time, any 

 physiological changes of importance. 



The most satisfactory results were produced by the action of 

 methyl-violet, which appears to penetrate and colour the proto- 

 plasmic mass, and to slightly dye the cell-wall. But when cells 

 thus coloured are well washed in distilled water and transferred to 

 a stain of aniline green for some hours, it is found that, in some 

 instances, the violet has only coloured the inner membrane of the 

 cell-wall, the outer layer having taken a slight green colour, which 

 enables it in favourable cells to be clearly made out. 



Where cells in process of developing buds, or having young 

 cells attached, have been thus double dyed, the observer is able 

 to ascertain with a great degree of exactness the manner in which 

 the budding takes place. It becomes clear that the distention of 

 the cell-wall at one point at length stretches the outer membrane 

 to such an extent that it becomes permeable to the mass within. 

 But no sooner has a small portion of the lining membrane or the 

 cell-contents found its way through, than the outer coat, relieved 

 of the pressure, closes by its elasticity around the protruded 

 portion, and causes it to assume the form of a globule, having 



