One means of effecting this consists in taking up with a pair of metallic forceps, previously heated, a piece of platinum wire, one or two centimetres (about 3/4 in.) in length, which we also pass through the flame of a spirit lamp, and with which, as soon as it is cold, we touch a mass of sporanges of a growth of _penicillium_. No matter how few spores may be taken up on the end of the platinum wire, we shall have far more than we require for the impregnation of the liquid. At the moment of charging the point of the wire we withdraw the glass stopper which closes the india-rubber tube on the right-hand neck of the flask (Fig. 14) and drop the wire through that tube; we then replace the glass stopper, after having, by way of additional precaution, passed it rapidly through the flame of the lamp. There is no doubt that we expose ourselves to error in consequence of having to convey the wire through the surrounding air, and also, in consequence of having previously to open the flask; but, as we have already remarked, this double cause of error has never, we may say, interfered with the exactness of our experiments, the volume of air with which we are concerned being exceedingly limited. Moreover, our flask being in free communication with the exterior air, by means of the opening in the curved, slender tube, there is no inrush of air when we withdraw the stopper. The chance of encountering a spore or fecund germ and introducing it into the flask on the wire that is charged with the others, is so remote that we have considered it unnecessary to adopt a more perfect apparatus, which might easily have been devised had we felt that it was necessary. A more serious cause of error may occur in the preceding method; resulting from the possible impurity of the spores taken from a field of _penicillium_ which has developed in contact with common air. This field receives, every instant, and has received throughout its growth, particles of dust which have fallen from the atmosphere; thus, it may not be, and, as a matter of fact, is not, free from the germs of other fungoid growths.[51] The operator, without knowing it, may frequently sow, besides the _penicillium_, which is all he can see, spores of _mucor mucedo_ and _mycoderma vini_, in short, of all the most common fungoid growths. [Illustration: Fig. 17.]