Hansen set himself the task of studying the properties of the varieties of yeast, and to do this he had to cultivate each variety in a pure state.
Pure Cultivation of Yeasts.-The methods which were first adopted by Hansen for obtaining pure cultures of yeast were similar in principle to one devised by J.
Hansen counted the number of yeast cells suspended in a drop of liquid diluted with sterilized water.
Hansen pointed out that this was by no means the case, for it is more difficult to separate the cells from each other in the gelatin than in the liquid.
Such, in brief, are the methods devised by that brilliant investigator Hansen; and these methods have not only been the basis on which our modern knowledge of the Saccharomycetes is founded, but are the only means of attack which the present-day observer has at his disposal.