To do anything like justice to the histological methods would require a volume in itself. When the sections are fixed upon slides, they are treated with a number of reagents to show their chemical and structural peculiarities. One section is stained specially to show the nucleus; another to show the centrosome; another zymogen granules, etc. And, as all these cannot be shown at their best in one cell, the differently treated sections have to be separately drawn or photographed, and the typical structure compiled from several. By careful staining, the chemical composition of the different parts of the cell is being worked out, and the effects of rest, activity, feeding, and other influences, studied. Take as an example the effects of a meal. A number of animals of the same litter are fed together out of the same trough. One has been killed before the meal, and the rest are killed at intervals dividing the time which must intervene before their next feeding-time comes round. Series of sections from their organs are prepared, one from each animal being mounted in order upon the same piece of glass, dipped in the same reagents, and examined under the same microscope. From a number of these sections the progressive effects of a meal upon each of the several constituents of the cell are traced out, and some of the chemical processes deduced. Turning to the physical side of physiology, it is unnecessary here to say more about the means employed for studying the properties of muscle and nerve than that many of the phenomena occur with such extreme rapidity that they can only be perceived by the photographic plate. In the study of the large organs, the physiologist finds a fascinating employment in devising models in which, so far as possible, all the physical conditions are reproduced, and this not only for the benefit of his pupils, but to help himself in perceiving their meaning. Too much reliance must not be placed on these models, of course, but they have added considerably to our knowledge of the eye and throat. It requires no great imagination to perceive the difficulties which lie in the way of studying the nervous system. Tracing nerve fibres under the microscope through interminable series of sections is a labour which can neither be hurried nor scamped. It is greatly aided by pathological specimens. An animal which has been through life with only one eye will obviously have central organs of vision showing wide contrasts. Those connected with the blind eye will be undeveloped, because never used, while the corresponding lobes of the brain connected with the other eye will show the effects of doing extra work.