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If, however, whole milk has been used in making the litmus milk the layer of cream that rises to the surface will be sufficient to ensure anaerobiosis; whilst if separated milk has been employed it will be sufficient to pour a layer of sterile vaseline or liquid paraffin on the surface of the fluid.

This last method is the most satisfactory for anaerobic cultivations, as by its means complete anaerobiosis can be obtained with the least expenditure of time and trouble.