On the Relations between the „Islets of Langerhans' etc. 63 



Fishes. Teleostei. Amiurus vulgaris, A. nigricans, 

 Catostomos teres, Hyodon alosoides, 

 Stizostedium vitreum, S. canadense, 

 Moxostoma aureolum. Es ox lucius. 

 Ganoidei. Acipenser ruhicundus. 

 Amia calva. 

 As for histological methods, very little need be said. Our most 

 general procedure has been to fix the perfectly fresh material in a 

 saturated acid solution of corrosive sublimate, embed in paraffin, cut 

 sections with a rocking microtome, fix sections by the distilled water 

 method on albuminized slides, and stain either in Delafield's haema- 

 toxylin or by Heidenhain's iron-haematoxylin method. Eosin or Orange G 

 has been our usual counter stain. 



Other methods, such as Flemming's fluid and iron-haematoxylin, 

 Flemming's fluid and Safranin and some of the special methods employed 

 by Laguesse^) have been used in special cases. 



II. Normal Histology of the Islets of Langerhans. 

 A. Mammals. 



The islets of Langerhans in the dog. 



The main features in the structure of the islets of Langerhans 

 are fairly well known and are indeed fairly well described in modern 

 text-books. Since, however, in our opinion several appearances are 

 usually over-looked or even misinterpreted, it will be well to give 

 some account of the structure of these „islets". 



Even with the low power of the microscope in stained prepara- 

 tions the islets stand out in marked contrast from the zymogenous 

 tissue. When the sections are stained by any of the ordinary histo- 

 logical methods the structures in question are visible as rounded, oval, 

 or irregular patches of very varying size. They are irregularly dis- 

 posed throughout the section, and are of markedly lighter tint than 

 the secreting acini, owing to the absence of the zymogenous granules 



^) Journ. de I'Anat. et de la Physiol. XXXIIe Année 1896, Nr. 3, Mai- Juin; 

 Archives d'anatomie micr., t. IV, fase. II et III, Nov. 1901; ibid, t. V, fascili, 1902; 

 C. R. Soc. de Biol., 4. août, 1900. 



