THE BLOOD. 117 



The enquiry having been proceeded with thus far, and the 

 stain having been proved to be one formed by blood, it stu 

 remains for decision, whether the blood thus detected is 

 human or not. 



In the solution of this difficulty the microscope likewise 

 affords considerable assistance, and this of a kind which can 

 be obtained in no other way. Although by this instrument 

 we are not able to assert positively from an examination of 

 the blood stain itself, free from admixture with any other 

 organic material, that the blood is really human, we yet shall 

 have it in our power very frequently to declare the converse 

 fact, viz., that a certain blood stain is constituted of blood 

 which is not human, a particular on the knowledge of which 

 the life of an accused individual might depend. 



Thus if we find that the blood globules are of a circular 

 form and destitute of nuclei, we may safely conclude that 

 they belong to an animal of the class Mammalia, although, at 

 the same time, we in all probability should not be able to 

 pronounce upon the name of the mammal itself; if, on the 

 contrary, the blood corpuscles are elliptical and provided with 

 a granular nucleus, we may be equally certain that they do 

 not appertain to that class, but either to the division of birds, 

 fishes, or reptiles. * 



By the size also as well as the form of the corpuscles, 

 some idea of the animal from which the blood was derived 

 might be formed ; and if we cannot pronounce with certainty 

 upon this, we shall at all events, and at all times, be able to 

 go the length of affording negative evidence, and of asserting 

 that the corpuscles do not represent the blood of certain 

 animals which might be named, and a knowledge of which 

 fact might prove of extreme importance. 



To show the valuable nature of the evidence which it is in 

 the power of a medical man who makes a right use of 

 the microscope frequently to afford, in criminal inquiries, 

 we will suppose the following case. 



* The only animals of the class Mammalia which have blood corpuscles 

 of an elliptical form, are those of the order Camelidce; they are, how- 

 ever, very small, and destitute of nuclei. 



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