THE HISTOGENESIS OF DENSE LYMPHATIC TISSUE 161 



This diversity of opinion among earlier investigators as to the 

 development of tonsillar lymphatic tissue (i.e., in the intestine) 

 and the practical omission of such study by more recent investi- 

 gators, together with the great amount of doubt and uncertainty 

 concerning questions of the origin and development of lymphatic 

 tissue in general, seem to warrant further study of the intestinal 

 tonsillar tissue (Peyer's patch and the appendix) in an attempt at 

 some interpretation of these structures. 



MATERIALS 



As material for the pursuit of such investigation, the rabbit was 

 considered as well suited, chiefly because of the great concentra- 

 tion and remarkable development of lymphatic tissue in Peyer's 

 patch in the lower portion of the ileum, causing an abrupt enlarge- 

 ment in it at its point of junction with the caecum, the sacculus 

 rotundus, or iliac tonsil (Muthmann, '13). 



Also, by use of this form, abundant material was easily obtain- 

 able in all stages of the development of these intestinal ton- 

 sillar structures. It was found after short study that in newborn 

 animals or earlier stages that there were no indications of the for- 

 mation of lymphatic nodules either in the region of Peyer's patch 

 or the appendix, so no embryonic material was collected. Fe- 

 males were secured, either in late pregnancy or just following the 

 birth of the litter, and the young rabbits removed from the 

 litter at desired intervals. The first indications of nodular 

 lymphatic tissue were found to be at an age of from two to three 

 days, free cells beginning to be massed in the location of future 

 nodules. From this time growth and differentiation proceed 

 at a rapid rate, until at an age varying from five to seven weeks 

 the nodules have assumed a structure like that found in the 

 adult individual (except for size). 



During this time of very rapid development, stages were 

 secured at very frequent intervals to be sure to get an uninterrup- 

 ted developmental picture. In practically all cases two or three 

 individuals of the same age were secured, to correct any devia- 

 tion which might occur in any single instance. Animals were 

 secured at daily intervals, and sometimes half-day intervals, 



