ORIGIN OF RED BLOOD-CORPUSCLES. 34l 
or else the nucleus undergoes a sort of breaking up, and its 
substance becomes dispersed in that of the protoplasmic 
body, so that it disappears altogether. This method, how- 
ever singular it may appear, I have distinctly proved to be 
the case. Such is certainly the origin of the first definite 
hsematids comparable to those of the adult which succeed 
the nucleated hsernatids. 
As to the transformation, or rather the haemoglobic de- 
generation of the protoplasmic body itself, it always goes on 
in the same way, the protoplasm becomes more and more 
homogeneous, more hyaline, more refractive. As long as 
the newly-formed hsematid remains immotile its true form 
remains obscured by the contact and pressure of the neigh- 
bouring elements. The hsematid is not really biconcave and 
discoidal either at the moment when it leaves or at the 
moment when it enters the circulation. 
Very soon after the rabbit^s embryo has attained a length 
of 22 mm. the vascular area ceases to be the seat of origin of 
the ha 3 matids. Lastly, it is interesting to note that during 
the whole of the first period of intra-uterine life globulets 
are not found in the blood, they only appear later on, and 
in abundance only in certain animals. 
Haematogenesis in the Adult . — Where are hsematids formed 
in the adult ? This is the great question which is occupying 
the attention at this moment of such a number of observers, 
and which has already been thought to have been solved 
over and over again. 
Usually observers have tried to relegate this so-called 
hjcmatopoietic function to certain organs or to certain tissues. 
I must now call special attention to these. This function in 
mammals has been successively attributed to lymphatic 
glands, to spleen, to the marrow of the bones, the lymphoid 
patches in the mesentery of the rabbit. There are yet the 
supra-renal capsules and thymus, do they also deserve to be 
studied from the same point of view ? 
Lymphatic Glands . — No hsematids are found in the lymph 
stream, the few which have been seen in fish are ex- 
ceptional, and probably came into it accidentally. Lymph 
taken from the thoracic duct of a dog, with proper precau- 
tions, never contains haematids, although in operating care- 
lessly on the horse the contents of the lymphatic vessel 
appear of a reddish colour ; this is due to the large quantity 
of haematids whose presence is caused by the careless oj)cra- 
tion. In the lymphatic glands the blood system is a closed 
system. Indeed, 1 have shown that it is not the same as the 
spaces constituting the lacunar tissue which makes a com- 
