^go Lymph Nodes, Thymus, and Spleen 



removed in a definite order by the same person to avoid variation in technique. 

 Upon removal from the animal, the tissues were placed in moist-atmosphere 

 weighing dishes and were weighed to the nearest milligram in a closed balance. 

 Care was taken to avoid drying of the tissues before and during weighing. The 

 technique remained the same for the entire series of autopsies. The data ob- 

 tained were analyzed to show means and standard errors of the means. These 

 data are presented in the form of tables, and further in the form of curves, 

 showing changes in organ weight for each age group. The body-weight aver- 

 ages included in the tables are not corrected for intestinal and bladder con- 

 tents, nor were the animals fasted preliminary to autopsy. 



A brief description is in order as to the technique of dissection of spleen, 

 thymus, and lymph nodes. The spleen was removed immediately after the 

 death of the animal in order to eliminate variation in weight due to changes 

 in the blood content of this organ. The spleen and thymus were dissected out 

 by simple severance of their connective tissue and vascular pedicles. Care was 

 taken in the case of the thymus to dissect away the associated lymph nodes. 

 Dissection of the cervical lymph nodes was carried out in the following man- 

 ner: a midline incision from the tip of the mandible to the sternum was car- 

 ried down through skin and superficial connective tissue. Reflection of the 

 skin flaps allowed exposure of the lymph nodes where they lie lateral to the 

 submandibular salivary glands along the line of the external jugular vein. 

 Incision of the overlying connective tissue allowed the enucleation of the well- 

 encapsulated nodes. The pedicles of the nodes were severed along the line of 

 the external jugular vein and the nodes were cleanly excised. There were 

 usually three separate and discrete nodes in the position mentioned. Included 

 in the nodes dissected was one deep cervical node from each side of the neck 

 (located dorsal and lateral to the omohyoid muscle where the latter crosses 

 the vascular sheath of the neck). The mesenteric nodes required relatively 

 more care in dissection. The procedure employed was to remove the entire 

 gastroenteric tract and associated viscera from the abdomen by simple section 

 of the mesenteries at the points of reflection upon the abdominal wall. The 

 liver was removed from the excised group of organs, and the entire mesentery 

 was carefully stripped away from the stomach and the large and small intes- 

 tines. Remaining was the mesentery (of the intestines and stomach) with the 

 associated vessels, fat, nerves, and lymph nodes. The mesenteric nodes were 

 found lying in a row along the root of the mesentery. By simple incision of the 

 overlying peritoneum the nodes were removed and freed from connective tissue 

 and fat. The nodes of the cervical and mesenteric regions were solid structures, 

 the cut surfaces appearing rather dry, there being little fluid accumulated 

 within the nodes. The dissection of the mesenteric nodes included groups 

 which may be designated as hepatic, gastric, intestinal, pancreatic, and cecal. 



The animals autopsied were examined for the presence of pathological con- 

 ditions. Animals suffering from gross evidence of respiratory or enteric dis- 

 turbances were excluded from the study. 



