THE BLOOD. 67 



and, in place of having a central depression, this part of each 

 globule is slightly protuberant. This prominence is due to 

 the presence of a nucleus, which in the mammalia we have 

 seen to be absent. 



The size of the red globules is as distinctive as their form, 

 it usually exceeding, in reptiles, three or four times that of the 

 majority of the blood corpuscles of mammalia. The blood 

 disc of the frog equals in length the yyV 5 ^ an i ncn > while 

 its transverse measurement is not less than the T ^3j f 

 an inch ; now the corpuscle of the elephant, the largest known 

 amongst mammalia, reaches only the gr^j of an inch in 

 diameter.* 



It has already been remarked that most of the animals 

 of the order Camelidce are possessed of blood globules of an 

 elliptical form, constituting in this respect an exception in 

 the class to which they belong. These oval corpuscles 

 are, however, so small that they could not be readily con- 

 founded with the elliptical globules of the frog, &c. : they 

 therefore agree in size, as well as in the absence of a nucleus, 

 with the blood corpuscles of other mammalia, although not in 

 form. While every possible care has failed in satisfactorily 

 demonstrating the presence of a nucleus in the blood of mam- 

 malia, not the slightest difficulty is experienced in detecting 

 it in that of the frog and most of the animals belonging to the 

 classes just mentioned, and therefore its presence is generally 

 recognised; although one excellent observer, M. Mandl, is 

 of opinion that its formation takes place subsequently to the 

 removal of the blood from the system : this idea is doubtless 

 erroneous, as we have seen to be the case with respect to the 

 white corpuscles of the blood, regarding which M. Mandl 

 entertained a similar notion. In blood corpuscles immersed 

 in their own serum, and examined immediately after their ab- 

 straction, the nucleus may be seen with a sufficient degree of 



* The largest blood corpuscles hitherto discovered in the animal king- 

 dom are those of the Siren and Proteus. In the Siren, according to. Mr. 

 Gulliver, the long diameter of the blood discs is the 435th, and the short 

 the 800th part of an inch, while in the Proteus they are stated at about 

 the 350th part of an inch in length. 



