130 NORMAL HISTOLOGY. 



on the part of a solution when separated from pure water "by a mem- 

 brane. Now, although the solids in lymph are less than those in 

 equal bulks of the blood-plasma, the lymph freezes at a slightly 

 lower point (about 0.02 degree C.) than the plasma, showing that 

 its molecular concentration is a trifle higher, and that there is a 

 tendency for water to pass from the bloodvessels into the lymph- 

 channels. This higher molecular concentration of the lymph is 

 attributed to cell metabolism, during which larger molecules are 

 abstracted from the lymph by the cells and smaller molecules — 

 i. e., molecules of less molecular weight — are returned to it. The 

 character of the lymph, then, will be affected by the metabolism of 

 the cells with which it comes into relation. These effects and differ- 

 ences in the capillary blood-pressure may be sufficient to account 

 for the differences in composition of lymph in various parts of the 

 body, so that secretory activity on the part of the capillary endo- 

 thelium is not necessarily a factor. 



The red corpuscles are soft, elastic discs, with a concave impres- 

 sion in both surfaces (Fig. 112). They are slightly colored by a 

 solution of haemoglobin, and are so abundant that their presence 

 gives the blood an intense red color ; but when viewed singly under 

 the microscope each corpuscle has but a moderately pronounced red- 

 dish-yellow tinge. The haemoglobin solution is either intimately 

 associated with the substance composing the body of the corpuscles, 

 called the " stroma," or it occupies the centre of the corpuscle and 

 is surrounded by a pellicle of stroma. 



Under normal conditions the red corpuscles, in man and most 

 of the mammalia, are not cells, for they possess no nuclei, nor are 

 they capable of spontaneous movement or multiplication. They 

 are, rather, cell-products, being formed either within the cytoplasm 

 of cells of mesoblastic origin, or by the division of cells derived 

 from the mesoblast, and called erythroblasts, the descendants of 

 which become converted into red corpuscles through an atrophy and 

 disappearance (probably expulsion) of the nuclei and a transforma- 

 tion of the cytoplasm into the stroma, which take place after the 

 elaboration of the fuemoglobin within the cell. The former, or 

 intracellular, mode of production occurs in the embyro, even before 

 the complete development of the bloodvessels; the latter mode of 

 production seems to be the only one occurring in the adult, the chief 

 location of the erythroblasts appearing to be in the red marrow of the 



