8 



THE BLOOD. 



given what seems to be the true explanation. He has shown that, shortly after removal 

 from the vessels, there exudes from the corpuscles an adhesive substance which smears 

 their surface and causes them to stick together. Of course the tendency is to adhere by 

 their flat surfaces. In examining a specimen of blood under the microscope, the presence 

 of this adhesive exudation may be demonstrated by employing firm and gradual pressure 

 on the glass cover, when the adherent corpuscles may be separated, in some instances, 

 and, with oblique light, we can see a little transparent filament between them, which 

 draws them together, as it were, when the pressure is removed. This phenomenon is due 

 to a post-mortem change ; but it occurs so soon, that it presents itself in nearly every 

 specimen of fresh blood, and is therefore mentioned in connection with the normal char- 

 acters of the blood-corpuscles. 



Dimensions. The diameter of the blood-corpuscles has a more than ordinary anatom- 

 ical interest ; for, varying perhaps less in size than other anatomical elements, they are 

 often taken as the standard by which we form an idea of the size of other microscopic 

 objects. The diameter usually given is -^^ of an inch. The exact measurement given 

 by Robin is .0073 of a millimetre, or ^^ of an inch. It is stated by some authors that 

 the size of the corpuscles is very variable, even in a single specimen of blood. We have 

 repeatedly measured them and found a diameter of g^inr f an inch. Very few are to 

 be found which vary from this measurement. Kolliker, who gives their average diame- 

 ter as s~frW f an mcn ? states that "at least ninety -five out of every hundred corpuscles 

 are of the same size." 



We cannot leave the subject of the size of the blood-corpuscles without a notice of the 

 measurements in the blood of different animals. This point is interesting, from the fact 

 that it is often an important question to determine whether a given specimen of blood be 

 from the human subject or from one of the inferior animals. Comparative measurements 

 also have an interest on account of a relation which seems to exist in the animal scale 

 between the size of the blood-corpuscles and muscular activity. In all the mammalia, 

 with the exception of the camel and llama, in which the corpuscles are oval, the blood 

 has nearly the same anatomical characters as in the human subject. In only two animals, 

 the elephant and sloth, are the red corpuscles larger than in man ; in all others, they are 

 smaller, or of nearly the same diameter. By reference to the table, it will be seen that, 



in some animals, the corpuscles are very much 

 smaller than in man; and, by accurate meas- 

 urements, we are enabled to distinguish their 

 blood from the blood of the human subject. 

 But, in forming an opinion on this subject, 

 it must be remembered that there is some 

 variation in the size of tlie corpuscles of the 

 same animal. We can easily distinguish the 

 blood of the human subject, or of the mam- 

 mals generally, from that of birds, fishes, or 

 reptiles; for, in these classes of animals, the 

 corpuscles are oval and contain a granular 

 nucleus. 



Milne-Edwards has attempted to show, 

 by a comparison of the diameter of the 

 blood-corpuscles in different species, that 

 their size bears an inverse ratio to the mus- 

 cular activity of the animal. Reference to the 

 table will show that this relation holds good 

 to some extent, while there certainly exists none between the size of the corpuscles and 

 the size of the animal. In deer, animals remarkable for muscular activity, the corpuscles 



FIG. 8. Blood-corpuscles of the frog ; magnified 370 

 diameters. (From a photograph taken at the 

 United States Army Medical Museum.) 



