Mr. G. Salmon on Theorems of Pascal and Brianchon. 49 



an opinion from the examination of one dog and one rabbit 

 (p. 37)*. 



Professor BischofFs book affords-a striking instance of the 

 truth of a remark made by myself long since; — viz. that with- 

 out a knowledge of the fact that the germinal vesicle returns 

 to the centre of the ovum, it is not possible to learn the mode, 

 the period, or the place of origin of the new being; or indeed 

 to understand the ovum in any of its future phases. 



In 1839 a note was added to my " Second Series" while 

 passing through the press, concerning Bischoff's contributions 

 to the plates accompanying R. Wagner's ' Physiology,' which 

 had subsequently come into my hands. My belief was there 

 stated that, while Bischoff's figures showed him to be in ad- 

 vance of others in his acquaintance with the mammiferous 

 ovum, they also showed that he had not obtained a suite of 

 early stages (" Second Series," I. c. t p. 354-). From the ani- 

 mus everywhere recognizable in Bischoff's book now under 

 consideration, it is evident that the opinion expressed in that 

 note has never been forgiven. What I then said, however, 

 I am now compelled to repeat, and to extend to Bischoff's 

 present communication on the ovum of the Rabbit. 



There is a word of counsel too, that I am under the neces- 

 sity of offering Professor Bischoff. When he professes to 

 communicate what has been done by others whose researches 

 have preceded his, and yet thinks proper, for some reason, 

 here and there to pass very lightly over, or altogether to omit, 

 certain portions of the history, — he should take care that, in 

 other parts of his book, none of these omitted portions are in- 

 advertently permitted to creep out. 



X. On the Properties of Surfaces of the Second Degree which 

 correspond to the Theorems (^Pascal and Brianchon on Conic 

 Sections, By George Salmon, Esq. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



[" PERCEIVE that you have inserted in your last volume 

 ■*■ [S. 3. vol. xxiii.] analytical demonstrations of the theorems 

 of Pascal and Brianchon on the Conic Sections. The two 

 theorems being connected by the theory of reciprocal polars, 

 it is sufficient to prove one of them, and for the best analytical 



* I sacrificed nearly a score of rabbits for the purpose of determining 

 the condition in which the ova leave the ovary; and was thus enabled to 

 show that the period of their discharge from this organ is very frequently 

 nine or ten hours post co'itum, an observation which Bischoff states to have 

 been confirmed by his own. (See my " Second Series," /. c., pp. 310, 3] 1.) 

 Phil. Mag. S.3. Vol. 24. No. 156. Jan. 1844. E 



