STUDIES ON THE GROWTH OF LYMPH NODES, 

 THYMUS, AND SPLEEN IN THE RAT 



Introduction 



EXPERIMENTAL and clinical observations on changes in size of the lymph 

 nodes, thymus, and spleen in various pathological conditions have sug- 

 gested the possibility of making comparative quantitative studies on the 

 growth and reaction of these structures to disturbances of an endocrine or 

 nutritional nature. 



In order to lay a foundation for studies of a quantitative natine on lymph 

 nodes, spleen, and thymus, it was thought advisable to follow the development 

 of these organs over a considerable part of the life span of the rat in order that 

 their behavior in disturbed physiological states might be inore intelligently 

 interpreted. The form of the growth curves for thymus and spleen have been 

 studied elsewhere in other strains of rats than the Long-Evans strain (Donald- 

 son,^ Chiodi,^'^ Plagge*). The present study is devoted to a comparison of the 

 growth in weight of thymus and spleen with that of the lymph nodes in the 

 Long-Evans strain. The growth in weight of these organs is followed in groups 

 of rats born at approximately the same time and autopsied at intervals over a 

 period of seven months. In addition, the reactions (in terms of weight changes) 

 of these structures to such stimuli as fasting, exposure to low temperature, and 

 endocrine imbalances are indicated to show the extent of weight loss which may 

 occtu^ in these structures. Histological studies are not included in this report. 



The studies of Job' have been of value in elucidating the location of the 



various grotq^s of lymph nodes in the rat. It was demonstrated by Job, and is 



confirmed by the present worker, that the lymph nodes in the rat are relatively 



constant in position and number. On the basis of unpublished experiments, 



the cervical and mesenteric nodes have been selected as representative of the 



lymph node tissue in the body. It is, of course, realized that the behavior of 



these groups of nodes may not be representative of all lymjDh nodes as a whole; 



generalizations may be applied only in a limited way to the other lymph nodes 



of the body. 



Materials and Methods 



Rats of the Long-Evans strain born in the last week of June and the first week 

 of July, 1941, were maintained under comparable environmental conditions 

 to the age of seven months. The animals received a regtdar ration (Diet XIV) 

 ad libitum, supplemented twice weekly with fresh lettuce. At varying intervals 

 during this time, groups of each sex were weighed and sacrificed under chloro- 

 form anesthesia followed by bleeding from the heart. Animals from the same 

 litters were sacrificed in different age groups to avoid peculiarities due to litter 

 groupings. The age at autopsy and the number of animals in each group are 

 indicated in the tables. The animals were then dissected, the tissues being 



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