ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 579 



unite to form them. Examples of growth by contact force are those 

 exhibited by artificial cells, in which the cell-membrane causes new 

 material to be taken up. Electrical contact gives another example ; 

 in a Daniell's cell, for example, electrical tension causes the accu- 

 mulation of oxygen and acid radicles at the zinc, of hydrogen and 

 copper at the copper pole, katenergic action taking place at the former, 

 anenergic at the latter point. The contact of living matter with dif- 

 ferent substances appears to this writer perhaps to cause electrical 

 phenomena which may be in part the source not only of nerve and 

 muscle activity, but also of the changes of the cell. The existence of 

 electromotive force at the poles of the cell-nucleus is perhaps shown 

 by the changes which it undergoes during cell-division, but chemical 

 agencies are probably also at work, so that the entire process is pro- 

 bably electro-chemical. 



Herr Bernstein considers some of his protoplasm-molecules to be 

 actually visible in the form of the " disdiaklasts " of striped muscle. 

 These are crystals, and thus exhibit the action of those molecular 

 forces which cause crystallization in inorganic matter. Haemoglobin 

 is another example of the same thing. A progressive development of 

 the fundamental molecules of living matter has probably gone on side 

 by side with that of the living organisms which they form, their 

 changes being promoted, as in those organisms, by the necessity of 

 adaptation to changing conditions. 



Hypotheses with regard to Perception of Light and Colour.* — A 



posthumous work by the late Franz Boll, whose brilliant investigations 

 into the physiology of the eye are well known, sums up his chief views 

 on the functions of the retina as follows : — 



He considers that the layer of this organ which is sensitive to 

 light " is composed exclusively of a very great number of separate, in- 

 dividual, and independent poiuts, every one of which is in immediate 

 contact with its neighbour. . . . These separate, independent 

 points I call ' sight-elements.' " He finds that each sight-element 

 possesses two marked properties, the one that of causing complete 

 perception of light and colour according to our ideas of these things, 

 the other a " local peculiarity," or special sensitive property peculiar 

 to each element. The separate elements have been recognized ; 

 they are placed at regular intervals. t,The peripheral retinal elements, 

 being imperfectly sensitive to light and colour, form an exception to 

 the first rule. The existence of the second property finds support 

 in many physiological facts and in some taken from the microscopic 

 anatomy of the sensory nerves, which show that a localized sensation 

 must travel for a long distance isolated in a primitive nerve-fibre ; 

 hence the number of local centres should be exactly that of the nerve- 

 fibres contained in the optic nerve. The actual sight-elements have 

 an anatomical as well as a physiological existence, but they are made 

 up of the pigment-cells, the rods, and the cones, and do not consist of 

 any one or two of these elements alone. This theory is supported by 



* Arch. f. Auat. et Physiol., 1881 (Physiol.) p. 1. Cf. Natnrforschcr, xiv. (1881) 

 pp. 220-2. 



