ON THE ORIGIN AND EARLY DEVELOPMENT OF THE LYMPHATIC 



SYSTEM OF THE CHICK, 



BY ELIOT R. CLARK AND ELEANOR LINTON CLARK. 



These studies were begun and partly carried out in Professor Mall's laboratory 

 in Baltimore, and have derived much from the inspiration of his enthusiastic and 

 kindly interest. We believe it safe to say that few problems in anatomy were of 

 as great interest to Professor Mall as that of the origin and mode of growth of the 

 lymphatic system. 



The numerous investigations and discoveries in this field during the past 

 twenty years were started with the epoch-making studies of Sabin in 1901, begun 

 at the instigation of Professor Mall and, almost without exception, can be attributed 

 indirectly to his guiding genius. It is an interesting illustration of his method of 

 achieving results that not one of the papers on the development of the lymphatic 

 system, published from his laboratory during this period, carries his name on the 

 title page; although, he might, with justification, have insisted that many of these 

 publications include his name as joint author. That he did not is evidence of his 

 pure unselfishness and his realization of the importance of developing early the 

 sense of independence, responsibility, and achievement in his students, if they, 

 in turn, were to become sturdy, independent anatomists. 



It is surprising to review the many changes in and additions to our knowledge 

 of the lymphatic system which have taken place since 1900, when Professor Sabin 

 began her studies. Previously, the conception of adult anatomy of the lymphatic 

 system was in a very hazy state. In fact, with the exception of the lymph-glands, 

 the thoracic duct, and other large lymphatics, it could scarcely be designated 

 as a real system, since it was supposed to merge, in obscure and devious ways, 

 with the peritoneal cavity, with the serous cavities in general, and with "spaces" 

 everywhere in the tissues. Even the discovery of von Recklinghausen (1862) that 

 silver nitrate stained the endothelium of lymph-vessels in a definite manner was 

 obscured by the faulty interpretation, which explained these silver markings as 

 revealing a sieve-like structure of the lymphatic wall, whereas they are now known 

 to represent cell-boundaries in a definite membrane. As for the embryology of the 

 lymphatic system, it was practically a virgin wilderness lighted only by the uncer- 

 tain torch of Budge's work, in which his injection of the extra-embryonic coelom was 

 interpreted as a picture of the primitive lymphatic system. 



To-day, less than twenty years after the beginning of the investigations in Dr. 

 Mall's laboratory years fraught with strenuous controversy at times presenting 

 seemingly irreconcilable views we possess an adequate knowledge of the structure 



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