August 4, 1916] 



SCIENCE 



149 



diffusible fluid should spread out into tissue 

 spaces and obscure the vessel — which is 

 most obviously not the case. Thus von 

 Becklinghausen 's discovery served to bring 

 up anew the question of open and closed 

 lymphatics. 



During the present century it has be- 

 come evident that some light might be 

 thrown on the obscure question of the rela- 

 tion of tissue spaces to lymphatic capil- 

 laries through the study of their devel- 

 opment. The first general hypothesis 

 concerning the origin of the lymphatic sys- 

 tem in the embryo was that fluid exuded 

 from the peripheral blood-vessels and grad- 

 ually hollowed out channels. As the fluid 

 increased, these vague channels were 

 thought to extend from the periphery to 

 the center and then establish connections 

 with certain veins. This hypothesis was 

 made concrete by Gulland, 7 who found 

 large empty vessels in the skin of embryos 

 about 4 cm. in length, which he thought to 

 be the first lymphatics. In reality the lym- 

 phatics begin much earlier. This general 

 hypothesis was to some extent modified by 

 studies of Budge 8 and Sala. 9 Budge in- 

 jected the extra-embryonal celom in early 

 chick-embryos, and got patterns of injection 

 in the area vasculosa vaguely simulating 

 lymphatics. These patterns we now know 

 were produced by fluid passing out of the 

 celom into the network of spaces between 

 the plexus of blood-capillaries. Budge then 

 made beautiful injections of true lymphat- 

 ics in much later stages, and to explain his 

 observations built up the hypothesis that 

 there was a primitive lymphatic system as- 

 sociated with the body cavity and a later, 

 secondary system of definite ducts. The 

 thoracic duct he believed formed the con- 



' Gulland, Jour, of Path, and Bact., Vol. 2, 1894. 



s Budge, A., Arch. f. Anat. u. Phys., Anat. Abth., 

 1887. 



9 Sala, L., Bicerche Lao. di Anat. Norm. d. r. 

 Univ. di Soma, Vol. 7, 1899-1900. 



nection between these two systems. These 

 observations of Budge, which we now 

 know to be incorrect, are, however, of great 

 interest to the embryologist — representing 

 as they do the earliest groping in darkness 

 in hope of finding the first lymphatics. 

 The work deserves emphasis also as the 

 only basis of all the erroneous theories sur- 

 rounding the idea that the body cavity is 

 in some especial way a part of the lym- 

 phatic system. 



Another very interesting attempt to find 

 the first lymphatics is shown in the work of 

 Sala, who studied the origin of the posterior 

 lymph-hearts in the chick. We know now 

 that these lymph-hearts arise as endothelial 

 buds from the walls of the coccygeal veins 

 and that these buds develop into a plexus, 

 which becomes a pulsating lymph-heart. 

 Sala, working with this rapidly developing 

 plexus, somewhat vaguely appreciated its 

 relation to the veins : he described a hollow- 

 ing out of cavities in the mesenchyme near 

 the veins and then said that in the last 

 analysis these cavities in the mesenchyme 

 were from their first appearance nothing 

 but terminal dilatations of the veins. How- 

 ever, he concluded that the lymphatics be- 

 gin as excavations in the mesenchyme which 

 soon join the veins. The confusion in 

 Sala's description is now easily understood. 

 Dominated by the theory that lymphatics 

 were tissue-spaces, he could not analyze the 

 evidence that they were from the start con- 

 nected with the veins, and so described them 

 as both veins and tissue-spaces. He made 

 it clear, however, that he believed that the 

 ducts were formed from chains of tissue- 

 spaces hollowed out in the mesenchyme and 

 lined by flattened-out cells. Sala's work, 

 however, places the first lymphatics close 

 to the veins, and demonstrates the diffi- 

 culties of relying on the interpretation of 

 sections in unraveling problems of growth. 

 Sala's work was published in 1900, and 



