NOTES AND MEMOKANDA. 183 



quently noted the same peculiarity with regard to Oscillatoriese that 

 had previously been observed in the case of diatoms : — that^ their 

 oscillating movements take place only when they are in contact with 

 a solid substratum. 



This explanation has up to the present time been a hypothetical 

 one ; but the extei'nal secretion of protoplasm, which Schultze, Siebold, 

 and Cohn had been unable to discover, has at length been detected by 

 Engelmann in the case of a large oscillatoria, Oscillaria dubia, Kiitz. 

 The method by which he at length succeeded was by passing induc- 

 tion currents through the water in which the alga was growing ; when 

 after a few seconds, an excessively thin coating, to which the foreign 

 particles were here and there attached, lifted itself from the surface 

 of the alga, but never to a greater distance than about * 008 mm. 

 The same took place after the careful addition of dilute potash, the 

 protoplasm subsequently entirely disappearing, which it did also 

 gradually on addition of dilute hydrochloric acid and 10 per cent, 

 solution of sodium chloride. With eosin and picro-carmine the thin 

 layer became distinctly coloured. The protoplasmic layer was also 

 subsequently made visible by the sudden addition of strong nitric 

 acid. It is probable that the immobile thread-like cilia, coloured 

 yellow by iodine, which had been detected in some Oscillatoriefe, as 

 Oscillaria viridis and Phormidium vidgare* may be portions of the 

 same external protoi^lasm. 



The Use and Abuse of Diatoms as Test Objects. — The following 

 remarks are not strictly new, but at the same time we do not remember 

 having previously seen the matter so well put. They occur in a paper 

 by Mr. Gr. D. Hirst, the secretary of the Section of Microscopical Science 

 of the Koyal Society of New South Wales (" Notes on some Local 

 Species of Diatomacese "), in the volume recently issued of that 

 Society's ' Journal and Proceedings ' : f — 



In conclusion, I would say a word in reply to questions I have 

 heard put sometimes, when, after the expenditure of much time, 

 trouble, and patience, adjusting of light and mirror, the lines on 

 some difficult test diatom have at last been fairly displayed: "Well, 

 what good have you accomplished? In what respect is microscopic 

 science benefited by the fact that such a diatom has so many lines to 

 the inch ? " There are, I know, many microscopists who affect to 

 despise those whom they call " Diatomaniacs," and count the time and 

 trouble expended in the resolution of markings as simply wasted. 

 Now, without for a moment arguing that the only or chief work for 

 the Microscope is counting the strife on diatoms, I would hold that 

 the time spent in successfully resolving a difficult test is by no means 

 wasted. The tyro, sitting down before his newly acquired instrument, 

 places an object on the stage, turns on the full glare of light from his 

 mirror and condenser, and fancies he sees everything to perfection. 

 Let him try the same method of proceeding on some delicate diatom- 

 valve ; and where in the hand of the skilful manipulator a moment 



* Nageli, in ' Beitr'age zur wissenschaftliclien Botanik,' vol. ii. (1860) p. 91. 

 t 'Journal and Proceedings of the Royal Society of N. S. Wales,' vol. xi 

 p. 272. 



