172 REMARKS ON THE GLOBULES OF BLOOD. 



same aspect : thus, those grouped together at the side have generally a 

 well defined circular line ; those entirely isolated, do not often show 

 where they are imperfect ; on the margin of the field there are globules 

 which exhibit this dark line well marked, and others where it is imper- 

 fectly visible. With very high powers, I have only observed rings, and 

 never dark central points within the globules. 



Every thing remains in the same state if the reflector be not moved, 

 and if the slide be not removed further from the eye-piece ; but when 

 the reflector is turned gently either one way or the other, at the 

 moment all the points or shaded rings may be observed to move and to 

 change their appearance ; for if the hand, or any other opaque body be 

 passed between the window from whence the light enters, and the 

 mirror which reflects the light upon the slide, the image of the hand or 

 other body becomes evident in the globule ; even if a small dark line or 

 point be made on the mirror, the same may be observed, if viewed atten- 

 tively, in each globule ; but more, when the globules are attentively 

 examined, it will be seen that in cautiously advancing and withdrawing 

 the object towards the body of the instrument, there are nearly always 

 some transparent globules of a more liquid character, in which may be 

 traced the image of the bars of the window more or less distinct. 



To form a correct idea of this phenomenon, and to be able to appre- 

 ciate its character, it may be well seen in very small globules of grease ; 

 but care must be taken in placing these small corpuscules slightly out of 

 focus, on account of the degree of refractive power of grease : here, in 

 the globules of grease, the annular series becomes confounded with the 

 the margin of the globules ; but it must be remembered, that they are 

 of a spherical form, and that the globules of blood are lenticular, 

 which gives rise to that partially destroyed (caustique) appearance 

 near the border of the latter. The same phenomena may also be seen 

 in small globules of glass and bubbles of air ; but modified by the diffe- 

 rent refractive power of these substances. 



Lastly, it is easy to be convinced that the shady ring seen in the 

 blood-globules under the microscope, is nearly always owing to an 

 optical illusion, produced by surrounding objects : I say nearly always, 

 because I do not pretend to assert that other causes might not give rise 

 to the same illusion ; as, for example, the depression which may be 

 formed by the diminution (retrait) of a globule losing its volume, when 

 the water with which it is impregnated evaporates. I do not further 

 doubt, that it is impossible to produce a true central nucleus, when, for 

 example, the surface of a globule absorbs the water in which it is placed 

 to examine it, and presents in consequence, a different degree of refrac- 



