WITH THE MICROSCOPE. 307 



may be examined by the highest magnifying powers yet made, by 

 which statement I mean, of course, to imply that more may be learnt 

 by the use of such high powers (1,000 to 3,000 linear) than by em- 

 ploying ordinary object-glasses. 



379. The Preparation of Embryonic Tissues for Examination 

 with very High Powers. Contrary to general opinion, many of the 

 softest textures may be investigated with the greatest facility after 

 having been soaked in strong glycerine. In preparing these, the 

 same steps which have been described in p. 300, must be carried out, 

 but the glycerine used at first must be weaker, and its strength must 

 be very slowly and gradually increased. Ova, at a very early period 

 of development, can be prepared according to the principles indicated, 

 and many important facts in connection with the first steps in the 

 formation of tissues demonstrated with accuracy. 



Some objections have been advanced by Dr. Ransom to this plan 

 of investigation as applied to the ovarian ova of fishes. Dr. Ransom 

 says, that the ammonia " dissolved the germinal vesicle and its 

 contents." Upon experiment, however, I found that so far from this 

 being the case, numerous nuclei were displayed, and many new facts 

 not to be demonstrated by examining the ova in water, were dis- 

 covered. In pi. LVIII, figs. 345, 346, have been copied from 

 Dr. Ransom's paper, while the remaining figures were taken from my 

 own specimens. See my paper, published in the Trans, of the Mic. 

 Society for July, 1867, from which pi. LVIII has been taken. 



Embryos of various ages may be injected with the Prussian blue 

 fluid. The pipe cannot be tied in the vessels, as they are extremely 

 soft. But if it is simply inserted, much of the injection will run 

 onwards into the capillaries, and the escape of a certain quantity by 

 the side of the pipe is a matter of no moment. 



It is often advantageous to harden the tissue slightly by the addi- 

 tion of a little of the chromic acid glycerine solution, p. 297. When 

 once the tissues have been fully permeated by glycerine, they may be 

 dissected and manipulated in a manner which before was impos- 

 sible, p. 294. 



In the same way, extremely soft textures, like those of which the 

 acalephas or jelly fishes are composed, or that delicate tissue entering 

 into the formation of the vitreous humour of the eye of man and the 

 higher animals may be prepared ; and all the masses of germinal 

 matter, or nuclei, which are very likely to be passed over in ordinary 

 methods of examination, most clearly demonstrated. The most 

 delicate infusoria and the germs of these and of the lower plants 

 may also be thus prepared and preserved. 



X 2 



