Dr. Crookshank is of opinion that, in the case of micro-organisms when their biological characters are studied under low powers of the microscope, photographs are preferable, because they give a more faithful representation of the object. A micro-organism, even under the highest powers of the microscope, is so minute an object, that to represent it in a drawing requires a very delicate touch, and it is only too easy to make a _picture_ which gives an erroneous impression to those who have not seen the original. Photography enables the scientific worker to record rapid changes, and it is quite possible as the art advances we may find the film more sensitive than the human retina, and that it will bring out details in bacteria which would be otherwise unrecognised. The result, therefore, of experience is that in research laboratories it will come into more general use as a faithful and graphic method. I cannot better bring these observations to a close than by giving a quotation from Dr. Piersoll’s practical method of obtaining micro-photographs. The three essential conditions to ensure success in micro-photography are:--(1) Satisfactory apparatus; (2) good illumination; (3) suitable preparations. With high amplifications (1,000 diameters and over), the conditions are greatly changed by the approach to the limit both of the shortness of the focus of the objective and of the length of the camera which can be advantageously used; for the first experience leads to the adoption of the 1/12-inch, for the second four feet is the limit, since a given high amplification, say 2,000 diameters, can be more satisfactorily and more conveniently obtained with a superior 1/12-inch connection with suitable optical means to increase the initial magnifying power of the objective, than with an unaided 1/25-inch lens, and the plate removed to a greater distance. Until quite recently the various amplifiers offered the best means of increasing the power of an objective, but the introduction of the _projection-oculars_ of Zeiss is an accessory piece of apparatus, far superior to any older device. These projection-oculars resemble ordinary microscopical oculars or eye-pieces only in general form and name, being optically a projection-objective in connection with a collecting lens. The new oil-immersion apochromatic lenses, in combination with these projection-oculars, form undoubtedly the more efficient equipment for high-power work; it is as true for high-power photography as for microscopical observation in general, that the best results are obtained with fine and necessarily expensive, optical appliances. If for the satisfactory study of the intimate structure of a cell, or of a micro-organism, the most improved immersion lenses are necessary, it is to be expected that, for the successful photography of the same, tools at least as good are needed. Sunlight certainly affords the most satisfactory illumination whereby good micro-photographs can