GENERATION. 



463 



gested to Spallanzani* the ingenious expe- 

 riment of artificial fecundation, which he first 

 performed, and which furnished the most con- 

 vincing proof that could be obtained, that, in 

 such animals as the frog, sexual union is not 

 essential to fecundation, and that, when the 

 ova are ripe and the seminal fluid of the suit- 

 able quality, the mere contact of the male and 

 female products is sufficient to confer fertility 

 upon the ova. 



Spallanzani opened very many female frogs 

 at the lime of propagation, but before they had 

 laid any spawn, and consequently before im- 

 pregnation could have occurred, and he satis- 

 fied himself that the ripest ova extracted from 

 the oviduct, and placed in water, gradually 

 passed into putrefaction without undergoing 

 any of the changes of development ; while some 

 of the same ova, upon which he had sprinkled 

 some of the seminal fluid taken from the body 

 of the male, and placed in similar vessels of 

 water, had tadpoles formed from them in the 

 same manner exactly as those which were fe- 

 cundated by the male frog itself.f 



The same experiments were performed by 

 Spallanzani on toads and newts with exactly 

 the same result. 



Spallanzani, in order to avoid every fallacy, 

 allowed the female to remain in union with the 

 male, and to lay her spawn in the natural way, 

 preventing only the access of any of the seminal 

 fluid of the male to the ova, by tying up the 

 hinder part of the male's body in oiled silk, and 

 these ova were alike barren, unless he added to 

 them some of the seminal fluid in the artificial 

 mode. 



TreviranusJ mentions the performance of the 

 experiment of artificial fecundation in Fishes, 

 viz. on the spawn of the Salmon, Trout, and 

 Carp, by Duhamel and by Jacobi. Jacobi's 

 experiments were repeated by Dr. Walker of 

 Edinburgh ; and very recently it has again been 

 performed on the spawn of the Tench and 

 Bleak by Rusconi of Pavia. (Cyprinus Tinea 

 and Alburnus.) 



The very complete series of experiments of 

 Messrs. Prevost and Dumas on the frog 

 afford the most satisfactory confirmation of 

 those of the Abbe Spallanzani. 



The following appear to be the more im- 

 portant results deducible from these two sets of 

 experiments. 



1st. That a very small quantity indeed of the 

 seminal matter is requisite for the fecundation 

 of the ovum. 



2d. That dilution of the seminal fluid with 

 water within certain limits does not impede, 

 but rather is favourable to its operation. 



3d. That the absorbent power of the albumi- 

 nous or gelatinous matter which surrounds the 

 black yolk is highly useful in bringing the 

 seminal substance in contact with the yolk, 

 where it is obvious its effect must be produced. 



* Dissertazioni di fisica animale, &c. 



t This experiment the author has more than once 

 performed with a similar result. 



J Erscheinungen und Gesezte des Organischen 

 Lehens. 



$ Annal. des Sciences Nat. torn. i. 



This albuminous covering, corresponding to the 

 white of the bird's egg, possesses the remark- 

 able property of absorbing water, somewhat 

 like gum tragacanth, in a determinate quantity, 

 and thus increases greatly in bulk after being 

 laid in water. In the experiments referred to, 

 the absorption of the water by the jelly was 

 fully demonstrated by the immersion of the ova 

 in coloured water, and it was found also that 

 the experiment of artificial fecundation suc- 

 ceeded best when the ova had not been im- 

 mersed in water for any considerable time pre- 

 vious to the addition of the seminal fluid. The 

 fecundation was less certain the longer the ova 

 were allowed to remain in water before the ad- 

 dition of the semen ; and it was shewn that this 

 did not depend simply on the length of time 

 of the separation of the ova from the body of 

 the parent, by the fact that ova taken from , 

 the oviduct and kept without moisture re- 

 tained their susceptibility of being fecundated 

 for a much longer period, as sixteen or twenty 

 hours. 



4th. That the seminal fluid of the frog retains 

 its fecundating power for about thirty hours 

 after it has left the body of the male. 



5th. Attempts were made by both the expe- 

 rimenters above quoted to ascertain, by way of 

 experiment, whether the seminal animalcules 

 are indispensable to fecundation. Spallanzani 

 came to the conclusion that the seminal fluid 

 did not lose its peculiar powers although de- 

 prived of its animalcules, or although the ani- 

 malcules were dead ; but it must be admitted 

 that the means employed by that observer to 

 ascertain the presence or absence of the seminal 

 animalcule were inferior to those we possess 

 in more recent times. Messrs. Prevost and 

 Dumas, who, it has already been remarked, 

 consider the animalcules as the most important 

 part of the seminal fluid in reference to its 

 fecundating properties, state that they found in 

 their experiments, that that part of the seminal 

 fluid which had been subjected to a very careful 

 filtration, and which had thus been wholly de- 

 prived of its animalcules, had lost all fecunda- 

 ting power, while the substance which remained 

 in the filter, and which was rich in animalcules 

 when diluted with water, possessed the same 

 powers of fecundation as the pure seminal fluid. 

 We think this experiment requires repetition 

 and some modifications, for other ingredients, 

 besides the animalcules of the seminal fluid, 

 might be retained on the filter. 



6th. Both Spallanzani and Prevostand Dumas 

 have attempted to estimate the quantity of 

 seminal fluid required for the fecundation of a 

 certain number of ova, and the latter observers, 

 pursuing their favourite idea to the utmost, have 

 even endeavoured to calculate the number of 

 animalcules which are necessary for the fructi- 

 fication of one or more ova. In Spallauzani's 

 experiments two grains of the semen of the 

 toad fecundated one hundred and thirteen 

 ova. Five grains of semen were mixed with 

 eighteen ounces of water; the point of 

 a needle dipped in this was made to touch an 

 egg for an instant and produced fecundation. 

 Hie proportion here might be estimated as 



