44 



two orders of birds is not greater than that now indicated between 

 the disks of two species of one natural family, the StrigidcB. 



" The corpuscles of the Snowy Owl, therefore, are very remark- 

 able and characteristic, as ahy one may immediately see who will 

 take the trouble to compare them with those of the Common Brown 

 Owl. I have examined the blood of several other species of this 

 family, and find the size and shape of the corpuscles of the Barn Owl 

 (Striw jiammea) to approximate most nearly to those of the Snowy 

 Owl. 



" It will be seen that the nuclei of the blood particles of the 

 Snowy Owl, exposed by acetic acid, were fully three times the length 

 of their breadth ; and it may be noticed incidentally, that in most 

 birds the nuclei thus exhibited have a more elongated ellipse than the 

 outline of their envelopes*. 



" We might expect to find an exact resemblance between the ele- 

 mentary parts of such a truly natural family as the Columbidce, and 

 yet the observations show a striking difference between the blood 

 corpuscles of the Passenger and Russet Pigeons, the average long 

 diameter of the former being 1-1 909th, and the short diameter 

 l-4626th of an inch, while the latter are 1-23 14th of an inch long, 

 and l-3429th broad. Although I have examined the blood of many 

 different species of the Columbidce, in no instance did the corpuscles 

 agree in figure with those of the Passenger Pigeon ; in the Turtle 

 Dove (^Columba Turtur) the long diameter appeared to be nearly simi- 

 lar, but the short diameter agreed with that observed in the disks of 

 the Russet Pigeon. Hence there was a remarkable difference in 

 shape, and the corpuscles of the Passenger Pigeon, as far as I have 

 yet ascertained, are quite peculiar, since the singularly narrow ellipses 

 which they present have not hitherto been found in the red particles 

 of other species of the Columbidee. 



" It should be recollected, however, that the results of my obser- 

 vations may exhibit differences rather apparent than real, since our 

 knowledge of the blood corpuscles is at present so limited, that we 

 are not sure whether their size and shape may not be subject to some 

 variation in relation to season, to the habits, or to certain conditions 

 of the animal. In Man, and some of the other Mammalia, I have 

 seen remarkable changes in the appearance of the blood corpuscles, 

 apparently in connection with disease ; and their size and shape are 

 undoubtedly liable to modifications, from the effect of causes which 

 have not yet been clearly explained. The observations recorded in 

 this paper have been made with so much care, to obviate any source 

 of fallacy, that I am disposed to place much confidence in the results ; 

 but even if it should ultimately appear that the differences which I 

 have described are not permanent, but merely within the limits of 

 variation to which the blood- disks are liable, this would be some 

 addition to our knowledge of these curious bodies, and would, at all 

 events, be sufficient to reconcile the numerous discrepancies appa- 

 rent in the measurements of various eminent observers. 



* See Dublin Medical Press, No. 59, March 4, 1840. 



