No. I.] BLOOD CORPUSCLES. 



6l 



Under certain conditions, however, as I shall endeavor to 

 show later, such as severe hemorrhage or ancemia from patho- 

 logical causes, some of the nucleated red corpuscles escape 

 from the blood-forming organ before the loss of the nucleus 

 has taken place. Neumann (5//) states that, in the pig, — un- 

 like other mammals, — one can always find in the normal adult 

 animal some few nucleated red corpuscles in the blood. I 

 have met with a similar exception in the opossum. In several 

 animals which I have examined I was able in each case to find 

 a few nucleated red corpuscles in the blood. 



The loss of the nucleus is one of the most important events 

 in the life-history of the red corpuscle, and has naturally been 

 the subject of much discussion. It is usually believed, as 

 taught by Kolliker (3), for the embryo, and by Neumann (5//), 

 for extra-uterine life, that the nucleus disappears within the 

 corpuscle by absorption, which may be preceded by fragmenta- 

 tion. I desire to come back to this subject under another 

 heading, and will not discuss it fully now. It is my belief that 

 the nucleus is lost not by absorption within the corpuscle, but 

 by migration or extrusion from the corpuscle, as shown in 

 Fig. 2. I mention this view at this time to call attention to 

 some evidence in favor of it found in the examination of the 

 blood of the young cat embryos of 2.5 cms. In the blood of 

 this embryo I obtained a number of specimens, such as are 

 shown in Fig. 2, in which the nucleus was seen in the act of 

 passing out of the corpuscle. This appearance has been seen 

 under different conditions by a number of observers, but has 

 usually been explained as a post-mortem change or as the effect 

 of mechanical pressure, action of reagents, or some similar 

 cause. Now, it seems to me that these explanations will not 

 hold in this case, because none of the nuclei of the large oval 

 corpuscles were found extruding, though they were submitted 

 to the same treatment exactly ; and, furthermore, amongst the 

 smaller true mammalian corpuscles, only those were found with 

 the nucleus extruding in which the nucleus stained a homo- 

 geneous tint with the methyl green. No nucleus showing an 

 intra-nuclear network was ever found escaping from the cell, 

 though there were many such cells in the preparation, and they 

 had passed through the same treatment as the corpuscles with 

 the other kind of nucleus. This last fact, as I shall show later. 



