AND ON THE DIRECT AGENCY OF THE SPERMATOZOON. 
245 
further, that the non-fecundation of the egg may depend much more on diminished 
vitality and inefficiency of the spermatozoon, than on the insusceptibility of the egg 
itself. 
5. QUANTITY OF SPERMATOZOA ESSENTIAL TO FECUNDATION. 
On a former occasion* I endeavoured to arrive at some conclusion as to the mini- 
mum quantity of spermatozoa necessary to effect impregnation, and to draw some 
comparison between the results obtained by myself and certain of the more remark- 
able ones by Spallanzani'!'. It then seeined to me, that although the general results 
obtained were in accordance with Spallanzani’s, yet that a larger proportion of fluid, 
and consequently a greater quantity of spermatozoa, was required than was supposed 
by him. I have, therefore, made further investigation on this subject, and have 
sought to obtain some knowledge of the quantity really necessary to fecundate the 
egg. Prevost and Dumas formerly made a similar .attempt^, and M. Quatrefages 
has recently done the same§. The results of the observations by Prevost and Dumas, 
Quatrefages, and myself, although differing greatly in detail, coincide with the general 
results obtained by Spallanzani, — that only an exceedingly small quantity of seminal 
influence, and consequently only a very limited number of vibratile spermatozoa is 
necessary to effect impregnation. They agree, too, in the fact that the number of 
eggs impregnated is always much fewer than that of the spermatozoa supplied to 
them ; and, consequently, that there is reason to think that fecundation is not the 
result of a single, isolated spermatozoon, although it has not been ascertained what 
is the number actually required. The course I have pursued in putting this curious 
question to the test, has been different from that of either of the distinguished 
naturalists mentioned. It has not been that of diluting the impregnating fluid in a 
very large quantity of water, and then applying a minute drop of the water to the 
Frog’s egg, as done by Spallanzani ; — nor has it been that of reckoning the number 
of spermatozoa on a given surface of a micrometer plate, and then immersing the 
plate in water with a quantity of eggs, and afterwards observing how many of them 
became fecundated, — the course followed by Prevost and Dumas ; — nor has it been 
by estimating the number of spermatozoa in a given bulk of fluid, and then ascertain- 
ing the number of eggs fecundated by them, as done by Quatrefages with those of 
the Hermella and Teredo-, but it has been by direct application of the spermatozoa 
on the point of a pin to the surface of a single egg in a glass cell ; and then observing 
beneath the microscope the number of spermatozoa deposited from the point of the 
pin, applied in a similar way as to the egg, on a plate of glass. Yet only approxi- 
mative results can be arrived at by this, or by the other modes of proceeding, 
although it is satisfactory to find that the general results obtained in this way are 
in agreement with those obtained by the observers mentioned ; and further, that the 
mode adopted has led to some additional results, which seem to be of value. 
* Philosophical Transactions, 1851, p, 206. t Dissertations, &c., vol. ii. p. 189. 
+ Annales des Sc. Naturelles, tom. ii. 1824. § Annales des Sc. Nat. 3™® sdrie, tom. xiii. p. 129. 
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