86 JOSE F. NONIDEZ 



use of Delafield's hematoxylin and eosin. If the sections be 

 stained previously with a 1 per cent aqueous solution of the lat- 

 ter stain (eosin W.g., Gruebler) and then with a ripe solution of 

 the hematoxylin, most of the eosin will be washed off when dehy- 

 drating through the alcohols, leaving only stained in brilliant red 

 the erythrocytes and the granules of the eosinophilic leucocytes, 

 whose distribution can be easily detected even under a low power. 

 The granules appear in deep black after staining with iron hema- 

 toxylin, which also reveals minute details in the structure of the 

 cells, such as the sphere, centrioles and earliest stages in the 

 deposition of granules in the cytoplasm. 



OCCURRENCE OF HEMATOPOIETIC FOCI IN THE GONADS 



In the mesenchyme of the chick embryo there is a widespread 

 tendency toward the production of blood-elements in certain 

 areas, which thus become hematopoietic foci. The mesenchyme 

 of the gonads being essentially similar to that present in other 

 regions of the body, it is not surprising to find the same phe- 

 nomena in these organs, leading to an active production of cells 

 which do not differ in any important respect from those found 

 elsewhere in the embryo. In the gonads the products of this 

 hematopoietic capacity of the mesenchyme are either temporary, 

 i.e., appear chiefly in the embryo or may share in the building up 

 of the tissue filling the spaces separating the seminal tubules and 

 ovarian follicles in the mature birds. Among the former, the 

 most conspicuous are the cells belonging to the myeloid group, 

 namely, those elements which contain acidophile granules in 

 their cytoplasm and become eventually eosinophile leucocytes. 

 The permanent elements belong to the lymphatic group and are 

 represented by considerable numbers of small lymphocytes scat- 

 tered through the stroma of the gonads after their production in 

 lymphatic nodules. In some cases, presumably under the influ- 

 ence of unknown physiological conditions, cells of the myeloid 

 group may also appear in the adult as the result of a myeloid 

 metaplasis of the connective tissue. 



