120 SUMMARY OF CURRENT RESEARCHES RELATING TO 



fibres and with coloured plates, showing their appearance when dyed 

 with turmeric yellow, iudigo blue, &c. 



The value of the Microscope with ordinary and polarized light, 

 and with dyed and undyed fibres, is throughout made a special featare, 

 and the book is to be welcomed as a noteworthy addition to the, at 

 present, very scanty literature relating to the practical applications of 

 the Microscope to manufactures. We should imagine that both silk 

 and woollen manufacturers would be benefited by similar treatises on 

 silk and wool. 



The limit of microscopical vision is, on pp. 156-7, treated as 

 synonymous with the limit of microscopical resolution, and in any 

 future references to the subject care should be taken to show that the 

 latter refers exclusively to the power, of distinguishing as separate two 

 lines or other objects close together, the limit of which is half the wave- 

 length in the medium employed x sin. u, whilst the vision of isolated 

 minute objects is only limited by the sensitiveness of the particular 

 observer's retina, the distribution of light, &c. Limit of " visibility " 

 is distinct from the limit of " visible separation." 



j8. Collecting, Mounting and Examining Objects, &c. 



Durable Preparations of Microscopical Organisms.* — Professor 

 G. Entz describes the method used by him for mounting microscopical 

 organisms. Protozoa, Eotifera, &c., preceded by an historical review 

 of the processes hitherto adopted. 



Ehrenbergf used a dry process which answered well only for 

 certain objects. Its use may be somewhat extended by soaking the 

 dried preparation in 1 part distilled water, 1 part glycerine, and (in 

 a large quantity) 1-2 drops of picric acid. The shrivelled parts 

 swell out and look very life-like. Amongst the organisms capable 

 of being so treated are the Volvocinese, Chlamydomonads, the lori- 

 cated Englence (E. acus and E. Spirogijra) Peridinete, the tests of 

 Rhizopods, tubes of Melicerta, Ciliata with resisting cuticles (as 

 Stentor igneus, Episfylis plicatilis, and fine chitinous elements, such as 

 the masticatory apparatus of Eotifera and small Nematodes. The 

 protoplasmic parts of organisms are of course entirely lost by this 

 method. 



Later still, Du Plessis | suggested glycerine coloured with chro- 

 mate of potash, and Duncker § in 1877 exhibited Eotifers, Protozoa, 

 and Algfe, which were highly commended by such authorities as 

 Cohn, Stein, and Leuckhart, and which showed the fine parts in a 

 most wonderful manner. Unhappily they were not permanent. In 

 a few weeks brown oily drops began to make their appearance in the 

 fluid, and ultimately the protoplasm also browned, so that they are 

 now useless. Duncker never published his method, but the author 

 considers it probable that the basis of the fluid he used was rectified 



* Zool. Anzeig., iv. (1881) pp. 57.5-80. 



t Abli. K. Akad. WIhs. Berlin, 183.5, p. 141 ; 1862, p. 39. 



X Arcli. f. Natuig., 1864, ii. Band, p. 162. 



§ See this Journal, i. (1878) p. 221. 



