156 BLOOD. 



sion. These solid particles consist principally of the blood-corpuscles, 

 with which, however, other formal elements are mixed, although in 

 far less quantity. Recent microscopic observations have revealed 

 to us the following facts in relation to the blood-corpuscles. 



The blood- corpuscles or blood-globules are distinguished by 

 peculiarities of form and size in every animal genus : in man they 

 are thick, circular, slightly biconcave discs consisting of a colour- 

 less investing membrane, and red, or, in refracted light, yellow, 

 viscid, fluid contents. Most observers at present coincide in 

 believing that these corpuscles have, except in rare instances, no 

 true nucleus, a very few occasionally containing an indistinct, 

 light granule in the concave centre. The blood- corpuscles of 

 other mammalia likewise form round discs, except those of the 

 Camel, the Dromedary, and the Llama, which are elliptic and 

 biconvex. In birds the corpuscles are elongated and oval, elevated 

 in the centre, and have a sharply defined outline ; in amphibia 

 they are oval and strongly convex. 



The human blood-corpuscles average about one three-hundredth 

 of a Paris line ( = 0'00333'" or 0'00752 mm ) in diameter. E. H. 

 Weber and R. Wagner have shown that in the embryo these 

 corpuscles are generally somewhat larger than in the same animal 

 after respiration has been established. The blood-corpuscles of 

 the mammalia approximate tolerably closely in size to those of 

 man ; they are, however, all somewhat smaller: those of the other 

 vertebrata, and especially of the amphibia, are, however, far larger 

 (ranging to 0'0142'" or T V") ; the largest occur in the blood of 

 Proteus auguinus. 



The difference in size of the blood-corpuscles of different 

 animals, is a point of the greatest importance in the investigation 

 of their blood, and is the more deserving of attention, since here, 

 as in so many other cases, chemistry entirely fails us, while the 

 microscope and micrometry yield the most decisive results. It 

 is at present utterly impossible to tell with certainty by chemical 

 analysis, to what species of animal a specimen of blood that may be 

 presented to us for examination belongs. For this object various 

 means have been devised, to which we shall, in a future page, at 

 all events make a passing reference ; but none of them yield 

 such decisive results in the majority of cases as the microscopico- 

 mechanical analysis. From what has been already stated, it is 

 obvious that by the microscope, and independently of all other 

 aid, we can readily distinguish the blood of the different classes of 

 vertebrata. C. Schmidt* has, however, shown that by accurate 

 * Die Diagnostik verdachtiger Flecke in Criminalfallen. Mitau und Leipzig, 1848. 



