REPTILES. 



tord, that the venous blood, becoming gradually lefs and 

 Icis dark coloured, approaches more nearly to the vivid red- 

 nefs nf the arterial itream. (Sec Philof. Tranfaft. v. 71. 

 p. 4!^7.) Haller obferved that there is no difTerence 

 between the arterial and venous blood in the frog. (Oper. 

 minor, v. i. p. 1S3.) And Spallanzani noticed the fame 

 faft in the falaniander or water newt : " avutafi egualita di 

 diametro, il colore del fangue venofo e fomigliantidimo al 

 colore del fangue arteriofo." De' fenomeni ilella circola- 

 iione, pag. 100. And again, " il fangue arteriofo in nulla 

 differifcc dal venofo, fia nel colore, lia nella dcnfita." P. 1 93. 



In this circumftance reptiles relemble the foetus of warm- 

 blooded animals ; in vs'hicli, fo long as it remains immerfed 

 in its uterine bath, we know that the arterial and venous 

 bloods are of the fame colour. 



Yet all animals of this clafs are not alike in this rcfpcft. 

 Accurate obfervers have aderted, that in the tortoife the 

 venous blood is black, and the arterial cfimion, as in the 

 warm-blooded claffes. (Caldefi, Ollervazioni Anatomiclie in- 

 torno alle Tartarughe, p. 60. Mery, Hill, de I'Acad. 

 des Sci. de Paris, 1669. v. 2. p. 210.) This difference 

 probably correfponds with the divcrlity of flructure obferv- 

 able in the refpiratory organs, which are calculated, in the 

 different orders of reptiles, to admit of a more or lefs inti- 

 mate expofure of the blood to tlio air in refpiration. 



The colour of the blood varies in our amphibia according 

 to the ftate of their nutritive functions : it is paler when 

 they have failed, of a deeper red when they have been 

 well fed. If, under the latter circumftance, it be drawn 

 from a vein, and expnfed to the air, it exhibits a bright 

 florid rednefs as it forms the coagulum. 



The component elements of the blood of amphibia, con- 

 fidered in a general way, feem nearly to refemble thofe of 

 the warm-blooded animals, except that in the former, when 

 examined alive, there are almoll always feen bubbles of air 

 mixed with their purple llream, performing, like the blood 

 itfelf, the circulation, and dividing that fluid in the vefTels 

 into intervals, as the mercury is interrupted in a badly made 

 thermometer. Redi and Perrault obferved this faft in tor- 

 toifes ; Jacobaeus in ferpents ; Daudin m the green lizard, 

 frog, and falainandcr (Hill. Nat. des Reptiles, Introd. 

 p. iSq..) ; and Blnmenbach in the amphibia of Germany. 

 Now, although in certain Hates the veins may be very 

 turgid, and elaflic air may be found in them after death, 

 nothing of this kind is ever known to take place in a healthy 

 and flrong individual. The air indeed is fuppofed in the 

 mammalia to conllltute one-thirtieth of the blood, but it is 

 fo diflblvcd, and fo intimately mixed in the vital llream, 

 that it can only be extricated and exhibited in its'elaftic 

 aerial form by artilicial means. 



The phenomena of the circulation are common on the 

 whole to the reptiles with the warm-blooded animals, and 

 are very familiar in the former, fmce the wonderful circulat- 

 ing motion of the blood was not only firll aftually feen and 

 defcribed in frogs by the great' Malpighi, but is alfo flill 

 examined to the prefent time in thofe animals. The branchise 

 of the tadpole are very favourable objefts for invcfligations 

 of this kind. 



As the circulation can be aftually feen in thefe animals, 

 we may inquire on this fubjeft, whether the globules of the 

 blood, entering the minute vefiels, can be really obferved to 

 change their figure, and become oval inftead of fpherieal. 

 " In warm-blooded animals," fays Blumenbach, " I have 

 never heard or read that any one has feen fuch a change ; 

 and I certainly have never feen, either in the incubated 

 chick, in which the circulation of ivarni blood may be moll 

 clearly and beautifully obferved, particularly on the fifth and 



Vol. XXIX, 



following days, or in the frog or lizird, any oval globulej; 

 yet Reichel alfcrts that he has feen globulei changed from 

 fpherieal to oval in the mefentery of the frog, and has 

 given an elegant plate in illuilration of the fact. See Ex- 

 pcrimcnta de Sanguine cjufque motu, fig. 3." Blumenb. 

 Specimen Phyfiol. p. 10. He doubts, liowever, whether 

 tl>is change can be confidered as a natural occurrence in the 

 healthy circulation, or ought to be referred to the diflurbancc 

 naturally following the futferings of the animal. 



The motions of the heart, conlifUng in our amphibia of 

 a flngle auricle and ventricle, agree in the alternate con- 

 tractions and relaxations of thofe parts, with the analogous 

 fucceflion of fyftolic and diaftolic changes obfervable in 

 the double auricles and ventricles of the warm-blooded 

 clafies. 



A quellion was formerly raifed, concerning this fyftole 

 or contraftion, whether the ventricles are really fhortened, 

 or experience merely a diminution of diameter ? The former, 

 fays Blumenbach, has now been proved by the mofl care- 

 ful obfervationsboth in cold and warm-blooded animals ; he 

 adds, that he has never feen it demonllratcd more clearly, and 

 beyond every fufpicion of inaccuracy or miilake, than in the 

 common fnake (coluber natrix), in fpecimensof which, two 

 yards long, from the woods of Germany, he has obferved, 

 and frequently demonftratcd, a Ihortening of the ventricle 

 equal to two lines. Blumenbach flatcs further, that the 

 ventricle is completely emptied in its fyitole, not the leafl 

 drop of blood flowing back into it from the aorta, in the 

 fnake, frog, and toad, and alfo in the incubated chicken. 

 But he does not venture to decide, whether the fame thing 

 occurs in man and the other mammalia, or whether the femi- 

 lunar valves may intercept fome drops of blood, which thus 

 are made to flow back into the ventricle. 



Reprodud'wn As the nutrition and growth of parts, in 



the healthy Hate, are among the mofl important fundlions of 

 the blood-veflels, fo the reparation of injury, and the reflo- 

 ration of what is mutilated, conflitute another very flriking 

 inftance of their powers, and a very imprefTive example of 

 thofe prerogatives, which belong exclufively to living orga- 

 nized beings. Although this power of reproduttion, taken 

 in its mofl extenfive acceptation, cannot be faid to be with- 

 held entirely from any animal, feveral genera of reptiles 

 poffels it in a more remarkable degree than any of the other 

 vertebral dalles. There is an intcrefling account in the 

 Memoirs de I'Acad. des Sciences de Paris, 1686, particu- 

 larly of the reftoration of the tail of lizards. Spallanzani, 

 Bonnet, and Blumenbach, have employed themfelves in 

 refearches oh this fubjeft. The former firfl called the atten- 

 tion of the public to it in his " Prodromo di uu' Opera da 

 imprimerfi fopra le Riproduzioni Animali." Bonnet pub- 

 lifhed his memoir on the reproduction of the limbs of the 

 water newt in the Journal de Phyfique, 1777. His en- 

 quiries were again pubHflied in his " CEuvres d'Hiftoire Natu- 

 relle," t. 5. and there are three memoirs by him on the fubjeft, 

 tranflated into Englifh, in Spallanzani's " Tracls on the Na- 

 tural Hillory of Animals and Vegetables," v. ii. The ex- 

 periments of Blumenbach are contained in his " Specimen 

 Phyfiologiae comparatat." The experiments have been made 

 chiefly with the water newt ; on the lacerta agilis of the 

 terreflrial kind, fee P. T. Hartmann, dubia de genera- 

 tione viviparorum ex ovo, p. 26 ; refpefting the lizards 

 of the Antilles, fee Oldendorp Gefchichte der Caraibifchen 

 MifTion, p. 97. 



" It might be fuppofed," fays Bonnet, " that the ampu- 



tation of the hmbs is mofl: painful, and that the animals 



would fuller long and feverely from it ; however, one of my 



obfervations apparently infers the reverfe. I cut the left 



% A hand 



