No. 2.] CHANGES IN THE SPLEEN OF THE FROG. 397 



every month, usually between the 7th and 15th, 12 frogs 

 (3 escidenta $, 3 csailcnta 9, 3 tanporaria $, 3 temporaria 9) 

 were selected for our purpose from the large number delivered 

 at the laboratory. Those of as nearly the same weight 

 as possible were selected. In order to avoid the effects of 

 captivity the frogs were collected the day before delivery 

 and killed on one of the two following days. The material 

 for all twelve months was not completed in the first year. 

 Advantage was taken of this fact in the succeeding two years 

 not only to supply deficiencies but also to increase the material 

 generally. 



The frogs were killed by cutting through the spinal cord 

 and then disturbing this and the brain with a needle. The 

 abdominal cavity was then cut open, the spleen laid bare and 

 so severed from the mesentery that it might fall directly 

 into a bottle of blood warm corrosive sublimate (concentrated 

 solution). The labeled bottles were placed in the warm oven 

 (39° C.) for 2 hours, after which the preparations were rinsed 

 in distilled water and left to stand covered with distilled water 

 in the oven for a half hour. They were then rinsed again 

 in distilled water and put into 70 per cent alcohol. The re- 

 mainder of the method for imbedding in paraffine is described 

 in Gaule's " Zahl und Vertheilung etc.," cited above. The 

 imbedded spleens were cut into sections about 2.5 to 

 5/ia1 thick with the microtome and fastened upon the slide 

 in the manner described in the same article. The paraffine 

 was dissolved with xylol, the preparation cleared with oil 

 of cloves and then brought into 100 per cent alcohol. The 

 sections were stained with the four coloring fluids, haematoxy- 

 lin. nierosin, eosin and safranin, in the same manner and 

 order described in " Methods of Staining and Fixing the Ele- 

 ments of the Blood," 2 except that sections require a different 



1 When the spleens contained large quantities of blood it was often impossible 

 to cut whole sections of ■^\^ mill, thickness. For the size measurements whole 

 sections were necessary, for the study of histological details the thin sections, 

 consequently I made one or two thicker sections of every spleen and many thin 

 ones. Care was taken to make sections through the largest diameters of the 

 spleens. 



2 Vide: American Naturalist, July, 1887, p. 677. 



