608 



SENSATION. 



of view, the representatives of the female 

 generative products the ova ; and that, as 

 explained in the commencement of our article, 

 we are enabled to pronounce the presence of 

 a particularly large quantity of liquor seminis 

 as a fact of subordinate significance in a his- 

 tological point of view. 



Under these circumstances we do not hesi- 

 tate any longer to coincide with Kolliker and 

 Bischoff* (the latter changed his opinion only 

 recently) " that it is the spermatozoa which, by 

 their contact, fructify the ovum." How this is 

 done remains as much an enigma as the real 

 essence, the remote cause, of every thing else 

 that is done. We are certainly able to watch 

 growing life in its first commencement, to 

 fathom the laws of the successive phases of its 

 developement ; but the internal relation of all 

 these processes is hidden from our percep- 

 tion. 



It is possible, and, indeed, even probable, 

 that the material constitution of the sperma- 

 tozoa is somehow concerned in fecundation. 

 Whether, however, as Bischoff supposes, the 

 act of impregnation merely takes place accord- 

 ing to the laws of the so -termed catalytic 

 power, that a certain internal motion is trans- 

 ferred from the spermatozoa to the molecules 

 of the ova, which till then were in a dormant 

 state, we do not venture to decide. At all 

 events, the circumstance, that it is not the 

 spermatozoa of every animal which are capable 

 without any distinction of fructifying every 

 egg, is sufficient in itself to prove that we 

 have not here to deal with such very simple 

 relations. It is an established fact, that only 

 animals of the same species enter voluntarily 

 into sexual connexion, and produce prolific 

 young ones. The importance of this law, 

 for the preservation of once created definite 

 forms of life, is evident. 



Exceptions to this law are but rarely 

 found, and generally are due to the interfer- 

 ence of man. Animals of a different species 

 scarcely ever enter into sexual connexion in 

 their natural state ; and, indeed, this act, 

 when it does take place under such circum- 

 stances, remains generally without any conse- 

 quences. Fecundation only takes place when 

 the respective individuals approximate to- 

 wards each other in point of genus, and even 

 then the hybrids produced are generally un- 

 fruitful. A fructifying act of procreation is 

 known in them only in very rare cases, and 

 that usually only when it takes place with 

 one of the original stock, not among them- 

 selves. 



This infertility or barrenness of the hy- 

 brids, coincides in a very interesting manner 

 with an imperfect developement of the sper- 

 matozoa, a relation which we might certainly 

 at once infer from the functional significance 

 of these formations. In many cases there 

 does not even seem to be any production of 

 spermatozoa ; a fact proved by the older state- 

 ments of Bonnet and G/eichen, as- well as by 

 the more recent researches of Prevost and 



* Mullet's Archiv. 1847, S. 436. 



Dumas*, as well as of Hausmann^ with 

 regard to the mule. One of us found the 

 same in the hybrids of goldfinches and 

 canary-birds. In others, real spermatozoa 

 develop themselves ; but they remain smaller 

 than in the stock species (^'" -V")* and 

 without the characteristic cork-screw spirals. 

 The thicker end is generally oblong, and fre- 

 quently curved at the point, or of an irregular 

 club form. In addition to this, the sper- 

 matozoa of the hybrids do not group together 

 in bundles, owing perhaps to their being 

 usually only small in number, even in the in- 

 terior of the separate cysts. The microscopical 

 examination of the semen in hybrids, the ca- 

 pacity of propagation of which has been con- 

 firmed, would be of importance. It is very 

 probable that the spermatozoa in these cases 

 have a regular developement, and their usual 

 form. 



BIBLIOGRAPHY. A. Leuwenhoek, Anatomia 

 seu Interiora Rerum, Lugd. Batav. 1687 ; Arcana 

 Naturae, Delphis, 1695 ; Epistolae Physiologic*, 

 Delphis, 1719 ; Sur les Animalcules de la Semence 

 des Animaux, Philos. Trans. 1672. Ledermuller, 

 Physikalische Beobachtungen der Samenthierchen, 

 Nuremberg, 1756. Spallanzani, Nouvelles Re- 

 cherches sur les Decouv. Microscop., Londres, 17G9. 

 Gleichen, Abliandlung iiber die Samen, und Infu- 

 sionsthierchen, Nuremberg, 1788. Prevost and 

 Dumas, Annal. des Sc. Nat. torn. i. ii. Czermak, 

 Beitrage zur Lehre von den Spermatozoen, Vienna, 

 1833. Treviranus, in Tiedemann's Zeitschrift, vol. 

 ii. Von Siebold, in Muller, Archiv. 1836, S. 232. ; 

 1837, S. 381. R Wagner, Fragmente zur Physio- 

 logic der Zeugung ; Beitrage zur Geschichte der 

 Zeugung und Entwickelung ; in den Abhandl. der 

 Konigl. Baeierisch Acad., Munich, 1837. Kolliker, 

 Beitrage zur Kenntniss, der Geschlechtsverhaltnisse 

 und Samenfliissigkeit wirbellosen Thiere, Berlin, 

 1841 ; Die Bildung der Samenfaden in Blaschen, 

 Nurembg. 1846. 



(^Rud. Wagner and Rud. Leuckart.) 



SENSATION. (Fr. Sensation; Germ. 

 Empjindung^) The improved state of our 

 knowledge of the physiology of the ner- 

 vous system makes it imperative that phy- 

 siologists should adopt and adhere to a pre- 

 cise definition of the term which forms the 

 heading of this article. 



Perhaps the simplest definition of sensation 

 which "can be given is the following ; namely 

 the perception by the mind of a change 

 wrought in the body. According to this 

 definition, then, sensation involves, first, a 

 bodily change, from some cause, whether in- 

 herent or external ; and, secondly, a mental 

 change, whereby the perception of the bodily 

 change is accomplished. A hot substance is 

 applied to the skin sufficient to burn ; a visible 

 change is produced on the part to which the 

 application has been made, shown by the in- 

 creased redness of the cutaneous surface, and 

 the nerves of the part are so irritated that 

 pain must be felt if the perceiving power of 



* Annal. des Sciences Nat. i. p. 182. 



f Ueber der Mangel der Samenthierchen bei Haus- 

 thierchen ; Hannover, 1844. 



J R. Wagner's Physiology, 20. Translation by 

 Willis, 12. 



