694 SUMMARY OP CURRENT RESEARCHES RELATING TO 



objectives in the same ratio as the refractive indices of the immersion 

 fluids (1-52 or 1* 33) exceed that of air(l'O). In the absence of 

 that knowledge, the benefit of oil over water necessarily seemed to be 

 very small — too small in fact to compensate for its disadvantages in 

 use. The appreciation, hovpever, of the increase in aperture — in the 

 delineating power of the Microscope — at once changed the whole 

 position and led to homogeneous immersion. 



In fact, to no class do the following words of A. De Morgan* 

 more aptly apply than to microscopists (italics as in original) : — 



" I have never found notice of any case of the theorem in any 

 writer prior to Cavalieri. For this occasion I have cursorily examined 

 the likely places of Maurolycus, Fernat, Sterinus, and Des Cartes, 

 without finding anything which ofifered a chance if the search were 

 pursued. But if, which is possible, any anticipation of a case or two 

 should be discovered or even the theorem itself, unapplied, I should 

 not the less give it the name of Cavalieri. I have come to a settled 

 conclusion that great points helong to those who made great 'points of 

 them. The history of mathematical discovery is vexed with never- 

 ending disturbances arising out of claims of priority, which mean that 

 this person threw the thing away before that person used it. In many 

 cases it is by no means certain that this person ever saw in his own 

 words or formulae what that person enables us to see. Giving due 

 moral blame to any one who consciously suppresses a hint which he 

 knows he has taken, I consider that an inventor who is the first user 

 has a position from which a hundred previous inventors cannot 

 dislodge him, nor do anything but enhance his merit as the 

 inventor of the use, most often the more difiicult invention of the 

 two." 



i8. Collecting, Mounting, and Examining Objects, &c. 



Colouring Living Infusoria, &c.t — M. A. Certes gives further 

 details as to the solution of cyanine which he makes use of for 

 colouring living infusoria.^ 



He finds that with a solution of 1 : 500,000 the colouring power 

 of the cyanine is still sufficient. Although stronger doses have been 

 used, they have never exceeded 1 : 100,000. As distilled water is 

 poisonous to infusoria, aqueous solutions of cyanine must be prepared 

 with ordinary filtered water. Whether the solutions are aqueous or 

 alcoholic, all decolorize more or less rapidly in the light, so that they 

 require to be kept in the dark. 



Unmixed Cultivation of different Bacteria. § — K. J. Salomonsen 

 has adopted the following mode of obtaining unmixed cultures of dif- 

 ferent putrefaction-bacteria. An absolutely pure sowing was taken 

 from putrefaction-specks in defibrinized ox-blood, which had been 

 preserved and observed in capillary tubes. In order to obtain as 

 large a number as possible of difierent forms, he chose (1) those 



* Trans. Camb. Phil. Soc, xi. (1866) p. 200. 



t Zool. Anzeig., iv. (1881) pp. 287-8. 



X See ante, p. 527. § Bot. Ztg., xxxviii. (1880) pp. 481-9. 



