ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 4:(')1 



Life of Peripheral Nerves in Plasma.* — Ragnvald Ingebrigtsen 

 has experimented with pieces of nervous tissue from young Mammals. 

 The Wallerian degeneration — i.e. the death and disintegration of the 

 axis cylinders and myelin sheath, which takes place in peripheral nerves 

 incubated in Ringer solution and serum — does not occur in plasma. 

 Peripheral nerves incubated in plasma give rise to no growth. The 

 same is true of peripheral nerves in Wallerian degeneration up to the 

 fourth day. Peripheral nerves in Wallerian degeneration from the 

 fifth day give rise to a growth of the syncytium of Schwann. In 

 cultures from later stages there is progressive growth of the same 

 structure. It is evident that the proliferation of the cells of Schwann 

 is directly produced by the degeneration of the axis cylinder and its 

 myelin sheath. In no case was growth of axis cylinders observed. The 

 growth of the syncytium of Schwann from degenerating nerves affords 

 a basis for an anatomical conception of the centrifugal orientation of 

 growing axis cylinders in regeneration. Morphologically there is a 

 striking resemblance between the syncytium of Scliwann and neuroglia 

 growing in plasma. 



Effects of Inanition on Thyroid and Parathyroid Glands of 

 Albino Rat.t— C. M. Jackson has observed the following changes in 

 young rats. The follicular epithelium is atrophied with reduction in 

 height. The nuclei are rarely hypochromatic (various stages of 

 karyolisis), but hyperchromatosis is more typical, the nuclei usually 

 presenting some stage of pycnosis. In the earlier stages the nucleus 

 may be nearly normal in size and structure, excepting a pale, 

 homogeneous coloration of the nuclear background. In more advanced 

 stages the nucleus diminishes in size, with deepened coloration, forming 

 a dense, deeply-staining, homogeneous mass (typical pycnosis). In 

 extreme cases the nucleus becomes fragmented (karyorrhexis). Neither 

 mitosis nor amitosis is found. 



The cytoplasm is usually reduced in amount considerably more than 

 the nucleus. It may show no marked change in structure (simple 

 atrophy), but usually becomes rarefied, with a marked vacuolization 

 (" hydropic degeneration ") and loss of the normal granulation. This 

 is especially marked in the few cells where the cytoplasm has lost but 

 little in volume. In some cases the cytoplasm may become homogeneous 

 ('.- colloid " type), and in advanced stages may disintegrate, forming 

 irregular, deeply-staining (eosinophile) masses of varied appearance. 

 The intrafollicular changes, which are not usually marked, are also 

 dealt with. 



In the adult rats the changes of the thvroid gland are in general 

 like those in the younger rats, )»ut the interpretation is complicated by 

 the fact that degenerative changes are frequent in normal (control) rats. 



The parathyroid glands appear to be relatively larger in the female. 

 They apparently belong to that group of organs in which growth 

 persists in young rats, even when held at maintenance (constant body 



* Journ. Exper. Med., xxiii. (1916) pp. 251-64 (8 pis.). 

 t Amer. Journ. Anat., xix. (1916) pp. 305-52 (14 figs.). 



