534 PHYSIOLOGY CHAP 



so that it remained as short a time as possible in tbe lymphatic 

 glands), or den'brinated arterial, or lastly venous blood from the 

 same animal. They showed that it was only after injection of the 

 lymph that decided modifications appeared in the curves of 

 arterial pressure and pulse frequency. The lymph obtained by 

 continuous massage thus contains specific substances that do not 

 exist in the arterial and venous blood of the same animal. It 

 is therefore probable that these are destroyed and modified in the 

 adenoid tissue of the lymphatic glands (in consequence, as it seems 

 to us, of the metabolism of the leucocytes accumulated there in 

 large quantities). Gabritschewski also put forward the suggestion 

 that the leucocytes absorb certain substances noxious to the body 

 by transforming them into innocuous substances, a phenomenon to 

 which he gives the name of pinocytosis. 



We must also assign a protective function, in the mechanical 

 sense, to the lymphatic glands, owing to their labyrinthine 

 structure, by which they function as filters to arrest, or at any 

 rate retard, the entrance into the blood of many pathogenic 

 microbes. This is proved by the fact that in miners, and also in 

 tobacco smokers, the reticulated tissue of the bronchial glands is 

 impregnated with pigment due to the particles of carbon intro- 

 duced into the bronchi with the inspired air. 



VIII. Among the lymphoid tissues Bone Marrow has acquired 

 a capital importance, ever since in 1865 Bizzozero in Italy and 

 Neumann in Germany discovered its haemapoietic functions. Three 

 different varieties of marrow can be distinguished : red marrow, 

 yellow marrow, and gelatinous marrow. The red marrow is found 

 in the spongy strata of the fiat bones and proximal epiphyses 

 of the long bones of the extremities (Neumann). Yellow marrow 

 is found in the adult in the distal epiphyses of the long bones 

 of the limbs, and is the result of infiltration and fatty degeneration 

 of the red marrow, which gradually increases with growth and old 

 age. In consequence of fasting, and in various morbid states with 

 general emaciation, the yellow is transformed into gelatinous 

 marrow, but does not lose its capacity for reconversion into yellow, 

 taking up fresh supplies of fat. 



Special interest attaches to the red marrow, which presents a 

 spongy mass, supported by reticular adenoid tissue (which, as 

 already stated, consists of fixed and ramified connective-tissue 

 cells and a rich plexus of branching blood-vessels). The nutrient 

 arteries that enter the bones divide at once into a number of 

 branches, which resolve themselves into a capillary network ; this 

 passes into a system of venous lacunae partly or wholly wanting 

 in organised walls, in which the blood moves very slowly; out 

 of this lacunar or cavernous rete arise the small veins by which 

 the blood flows out. It is notable that the veins that occur 

 within the medullary tissue are wholly deprived of valves, while 



