220 SUMMARY OF CURRENT RESEARCHES RELATING TO 



sion of the primary nuclear filamcuts, and according to the kind of 

 union that they or their outgrowths make ; in other words, there is 

 a great variety in the possible structural relations of the resting 

 nucleus ; it is quite conceivable, although it has not yet been shown, 

 that definite form-stages of the nuclear network always correspond 

 to definite functional stages of the nucleus. And it further appears 

 quite possible, and, indeed, probable, that if in a resting nucleus wo 

 can observe only sharply separated chromatin-masses, but no chro- 

 matic nuclear plexus, the remains of the primitive filaments have 

 become retrograded into delicate hypoplasmatic cords. 



In these general considerations Eabl has left out of view the 

 nuclear spindle, inasmuch as w^e do not yet know what it signifies, 

 but it is probably the expression of streaming movements, the poles 

 being centres of attraction. 



Formation of Red and White Blood-corpuscles* — M. Lowit finds 

 that the red blood-corpuscles are developed from formative cells 

 ■which are free from hasmoglobin, and become imjiregnated with it 

 during the course of their development. They increase by indirect 

 nuclear- or cell-division, and are to be found abimdantly in the sjdeen of 

 Tritons in the spring ; in the circulating blood of these animals some 

 formative cells are to be found in various stages of indirect nucleus- 

 division ; the great number present in the spleen makes it probable 

 that that organ is the chief, though not the sole seat of their origin. 



Among the Mammalia the liver is more important than the spleen ; 

 in later stages of development, when the osseous medulla is deve- 

 loped, it appears to be the most important point of origin of the red 

 blood-corpuscles. The nucleated red blood-corpuscles of the embryo 

 are converted into non-nucleated by the gradual disappearance of the 

 nucleus of the cell. The nucleated red blood-cells of adult animals 

 agree in structure with similar elements in the embryo ; they are 

 most common in the osseous medulla, though found scattered in the 

 spleen and lymphatic glands. 



White blood-corpuscles are to be found in abundance in the spleen 

 of Triton ; in mammalian embryos the liver contains a large number 

 of them, and in later stages they are numerous in the thymus, the 

 spleen, the lymphatic glands, and the osseous medulla. They are 

 sharply distinguished from the red cells by their structure ; no inter- 

 mediate stages between them can be demonstrated, and the structure 

 is so different as to make it impossible for us to think that one could 

 be converted into the other. The white cells exhibit direct cell- 

 division only. The differences in the sizes of white blood-cells may 

 be regarded as the expression of a continuous development. In some 

 cases we observe polymorphic nuclei, which are probably due to 

 degenerative division, which may jiossibly lead to a complete karyo- 

 kinesis. The term polynuclear white blood-cells should be reserved 

 for those forms in which two or more nuclei are to be seen, or where 

 direct division can be observed. The author concludes with some 

 reflections as to the bearing of his observations on leukaemia. 



* SB. Akad. Wiss. Wion, Ixxxviii. (1884) jip. 350-401 (2 pis.). 



