« GRANULE-CLUMPS » AND SPIRUCHAETES 53 



cîumps under dark-ground illuminalion. Thèse were most 

 readily observed in cnished porLions of a Malpighian tubuleor 

 of an ovaiy suspended in a drop of saline solution. At first it 

 was by no means easy to be certain of the identity of any 

 particuiar groiip of granules seen against the darkbackground, 

 but it soon became possible to recognise them by attention to 

 certain points. In the first place, the size, number and form of 

 the granules composing a clump were more or less uniform; 

 secondly, the brightness and yellowish-white colour of the light 

 refracted by the granules was more or less characteristic and, 

 thirdly, the granules were seen to be embeddedina welldefined 

 but faintly refraclile matrix, an appearance only occasionally 

 noted in stained spécimens. This last point appears to me of 

 some significance as suggesting thatthere is some vital connec- 

 tion between the différent portions of the clump, in opposition 

 to the view that the granules are merely held in apposition 

 by physical attraction. The appearance of the clumps is 

 illustrated in fig. 1, n°' 1-6. 



In this connection I may mention a point of some technical 

 utility which I hâve noted in the course of thèse observations, 

 and which is apparently unknown to other workers. It is 

 usually assumed that the use of the dark-ground method of 

 illumination is limited lo moist or tluid préparations. I find, 

 however, thatit is quite possible to examine a dried and stainèd 

 film, for example, a film prepared from some organ or tissue 

 of a tick and stained by Romanowsky, to note from this aU 

 that can be learned as to the detailed structure of some cell or 

 parasite and then, leaving the spécimen in position on the stage 

 of the microscope, to change the illuminating System for the 

 dark-ground method. It will be found that the resulling 

 picture differs very slightly from that which would hâve been 

 given by the same structure if ithad been examineil, unslained' 

 in a tluid médium. The refractility of the différent éléments 

 appears little altered and the colours produced by the staining 

 bave only a slight modifying influence on the white reflex of 

 light refracted from the object. By this proceedure it was 

 possible to détermine the staining reaction of a particuiar 

 granule or granule-clump and then to investigate its refracting 

 power by dark-ground illumination. This method I bave found 



