398 GAULE. [Vol. VIIL 



length of time to absorb the staining fluid. Haematoxylin, 

 according to its freshness, demands from 5 to 10 min., nigrosin 

 2-5 sec, eosin 2-5 sec, safranin 5-10 min. Care must be 

 taken not to leave the preparations in absolute alcohol too long 

 after treatment with safranin as this color and eosin are very 

 soluble in alcohol. The further treatment is also described in 

 the same article. The material was then ready. A general 

 inspection of the spleen showed that not only the size of the 

 spleen, but also its general and detailed histological character, 

 varied from month to month. Individual frogs, in turn, varied 

 frequently in the same month, still the impression was that 

 the variations were subject to certain laws, and so, owing to 

 the vast material, — the spleens of over 150 frogs — I decided 

 to arrange notes and measurements in the form of curves. 

 The months of the year formed the abscissa in every case, the 

 measurement, number, or proportion respectively the ordinates. 

 The curves were made at first for every separate spleen being 

 grouped under four heads esculeiita Z and 9 and tcmporaria 

 t and 9. Later the average curve under each head was 

 computed for every month. They were computed by adding 

 the individual curve for every spleen for the month and dividing 

 this result by the number of spleens investigated for that 

 month. 



General Structure of the Spleen. 



The spleen of the frog has an outer fibrous covering which 

 varies in thickness in different frogs. The large splenic 

 artery enters the spleen at the same point that the splenic 

 vein leaves it. The arterial blood is carried nearly to the 

 centre of the spleen by the artery which then divides into 

 endless capillaries and meshes extending nearly or quite to 

 the fibrous capsule. Here the meshes often become wider 

 and are sometimes seen to form a vein which can occasionally 

 be followed along the inner surface of the capsule and probably 

 enters the splenic vein. A large vein is also frequently seen 

 returning along the splenic artery. The spleen of the frog has 

 no distinct trabeculse like those of mammals. This is about 

 all that can be said to be quite constant in the spleen of every 



