by the Method of Dark-ground I Humiliation. 603 
particles of microscopic size in suspension (Perrin, ’13), and shown by 
Zsigmondy to extend to these ultramicroscopic particles, where the pheno- 
menon is manifested as a much more vigorous motion — ‘ like a swarm of 
dancing gnats in a sunbeam’ (’09, p. 134 ). The phenomenon has been the 
subject of some fine researches by Perrin (1. c., T3), who has shown, almost 
beyond doubt, that the movement is to be regarded as an outcome or 
manifestation of the activity of the ultimate molecules of the continuous 
phase. It has been suggested that, on account of the great activity of the 
movement for ultra-microns, the phenomenon should in this case be termed 
the Brownian Zsigmondy movement (Bechold, ’ll, p. 43 ). 
Besides the work of Gaidukov, comparatively little has been done with 
the method in the particular direction of the study of the plant cell. A short 
preliminary note (Price, T2) was published some time ago containing an 
account of a few of my observations with the method ; most of these are 
amplified in the present paper. 
Ruhland (T2, p. 376 ), in his researches on the behaviour of the plasmatic 
membrane as an ‘ultra-filter’ (Bechold/ 11, p. 86 ), has made use of the 
method to a certain extent, chiefly in the study of the size of particles in 
certain dyes or stains, and to examine the process of the taking up of these 
through the plasmatic membrane. 
Other observations have been made which are somewhat akin but are 
not actually botanical in nature. Thus the observations of Faure-Fremiet 
(TO) on the nucleus of certain Protozoa is of, interest and is referred to 
below. 
§ 2. The Present Work. 
The work which is at present described was undertaken with the idea 
of testing the possibility, by the use of the method, of getting some more 
facts concerning the colloid structure of the living and dead cell, of studying 
the reactions of the colloid, and so on. There is undoubtedly a great deal 
of work to be done in the study of the physiology and properties of the cell 
itself, as this is, after all, the unit which has to be considered in general 
physiological processes, and, following the work of Gaidukov, it seemed 
that something in this direction might be expected of the method of dark- 
ground illumination. 
As the method is a comparatively new one, some of the results here 
described are to be taken as special cases indicating lines of study which 
might be increasingly productive in the future, and so in many cases it is 
impossible to draw general conclusions from them. 
Practically the whole of the work has been done in the Botany School, 
Cambridge, during the tenure of the Frank Smart Studentship. I should 
like to take this opportunity of thanking Prof. Seward for granting me all 
facilities for the work and for encouragement during its progress. To all 
