BED GLOBULES OF THE BLOOD. 253 



LONG DlAMKTEK OF THE OVAL RED GLOBULES OF BlRDS, REPTILES, AND FlSH, 



in micro-millimetres. 



Pigeon .... 147 Frog ...... 22.0 



Fowl . . . . . 12.1 Triton 29.3 



Duck 12.9 Menobranchus . . . 62.5 



Tortoise .... 20.0 Carp 13.1 



Lizard .... 16.4 Sturgeon .... 13.4 



Alligator 19.2 Perch 12.0 



Diagnosis of Blood, and the distinction between Human Blood and that 

 of Animals. It is often of consequence to recognize the existence of 

 blood in various animal fluids in physiological experiments, and it some- 

 times becomes important in medico-legal investigations. For this 

 purpose, in the fresh fluids, nothing can be more satisfactory than 

 spectroscopic examination ; a very small quantity of hemoglobine, as 

 already shown, being sufficient to yield a spectrum with the character- 

 istic absorption bands. There is a further advantage in this method, 

 namely, that it will enable us to detect the presence of blood in fluids 

 where the red globules have been dissolved and the coloring matter 

 reduced to a fluid condition. The washings of a blood spot or stain 

 may therefore show the spectrum of hemoglobine, although they may 

 not contain any red globules perceptible by the microscope. This, how- 

 ever, only shows the presence of the coloring matter of blood, and thus 

 allows us to distinguish blood from other colored fluids ; it does not 

 enable us to make a distinction between the blood of man and that of 

 animals, since the hemoglobine is the same in all. 



But by microscopic examination of the red globules, either when 

 fresh or after having been dried and again moistened, we can often dis- 

 tinguish the blood of an inferior animal from that of the human subject. 

 According to the observations of Prof. J. G, Richardson, 1 a fragment of 

 a blood spot, weighing less than r -|^ of a milligramme, which had been 

 kept in the dried condition for five years, when decolorized with a weak 

 watery solution (0.15 per cent.) of sodium chloride, and afterward tinted 

 with a solution of aniline, exhibited the blood-globules in such a condi- 

 tion that their size could be accurately measured. 



If a blood stain, accordingly, which in a watery solution gives the 

 common spectrum of hemoglobine, be found to contain oval nucleated 

 globules, this would show it to be the blood of a bird, reptile, or fish ; 

 and the oval form alone would show that it is not human blood. The 

 question, therefore, whether a particular specimen be composed of human 

 blood may often be. decided with certainty in the negative by microscopic 

 examination. But if the specimen contain circular globules, without 

 nuclei, it will be impossible to say positively, in any instance, that they 

 belong to human blood, and not to that of some animal, such as the ape 

 or the dog, whose red globules nearly approach the human in size. In 

 most of the domesticated quadrupeds, the globules are smaller than in 



1 Monthly Microscopical Journal. London, September 1, 1874, p. 140. 



