20 SUMMARY OF CURRENT RESEARCHES RELATING TO 



for the study of the canaliculi, and show clearly that prolongations of 

 the surrounding stellate interstitial cells penetrate into the cytoplasm, 

 and there ramify to form a network. These prolongations are hollow, 

 and their ramifications therefore constitute a network of canaliculi. 

 which open externally into the meshes of the interstitial tissue. Such. 

 a system of canaliculi also occurs in the axis-cylinders of nerves, but 

 a notable difference in the latter is the absence of the " tigroid " sub- 

 stance found in nerve-cells. The author's preparations showed the 

 inter-relation of nerve-cells and interstitial cells so clearly, and shed 

 so much light on his other previous preparations, that he considers that 

 the cells of the Metazoa generally may be divided into two sets, accord- 

 ing to the nature of the canaliculi. The two main categories of cells 

 are then as follows : — (1) Cells of high physiological significance, which 

 are not simple but of complex organisation, and consist of central cells 

 provided with a trophic mechanism presided over by subsidiary cells. 

 Examples are nerve-cells, muscle-cells, reproductive cells, certain gland- 

 cells. (2) Cells of lower physiological importance, which may possess 

 canaliculi, but have not a trophic mechanism dependent upon subsidiary 

 cells. The distinction he believes to be of primary importance. The 

 paper is illustrated by some striking figures of the nerve-cells of the snail. 



Structure of Human Neuroglia.* — Dr. A. J. Aguerre has confirmed 

 the Ranvier-Weigcrt view as to the minute structure of the neuroglia, 

 and has further made some novel observations on the nuclei of the glia- 

 cells. While Weigert speaks only of two kinds of nucleus, large vesi- 

 cular forms with granular chromatin, and small rounded forms with 

 homogeneous chromatin, the author's preparations showed pronounced 

 polymorphism of the nuclei. All possible shapes were present, e. g. 

 spindle-shaped forms, three-cornered, hourglass-like, &c, the most in- 

 teresting perhaps being curved forms not unlike the nuclei of certain 

 leucocytes. There was also a considerable variation in size, the range 

 being from 3-14 /x. Further, some of the nuclei showed clear indica- 

 tions of increase by amitotic division, which the author regards as proof 

 that the glia-cells increase in number. He holds strongly that the 

 neuroglia is actively functional, and is not merely a passive supporting 

 substance. 



Islands of Langerhans in Pancreas.f — Walter Schulze briefly re- 

 views the literature of these structures, and points out that the real 

 question in regard to them is whether they are to be considered as 

 modified parts of the pancreas, or as structures sui generis. He made 

 a series of experiments on guinea-pigs by isolating a small fragment of 

 the pancreas with a ligature, the object being to determine whether or 

 not the " islands " and the other portions of the pancreatic tissue would 

 behave alike. In all cases ho found that while the ordinary pancreatic 

 tissue underwent progressive atrophy, the islands remained unaffected. 

 This points to the conclusion that the islands are independent struc- 

 tures, not related to the duct system of the pancreas proper. Again, 

 reasoning from such pathological phenomena as pancreatic diabetes 

 leads to the conclusion that the islands are blood-vessel glands of the 



* Arch. Mikr. Anat., Ivi. (1900) pp. 509-25 (1 pi.). 



f Tom. cit., pp. 491-509 (1 pi.). Cf. this Journal, 1900, pp. 25, 308. 



