THE BLOOD. 169 



nervous system in raammals, and especially in man, has an in- 

 fluence over the formation and fate of the blood generally, is 

 scanty, there can be little doubt that such is the case, when we 

 take into account instances that frequently fall under the notice 

 of physicians. Certain forms of anaamia have followed so di- 

 rectly upon emotional shocks, excessive mental work and worry, 

 as to leave no uncertainty of a connection between these and 

 the changes in the blood ; and the former must, of course, have 

 acted chiefly if not solely through the nervous system. 



It will thus be apparent that the facts of disease are in har- 

 mony with the views we have been enforcing in. regard to the 

 blood, which we may now briefly recapitulate. 



Summary. — Blood may be regarded as a tissue, with a fluid 

 matrix, in which float cell-contents. Like other tissues, it has 

 its phases of development, including origin, maturity, and 

 death. The colorless cells of the blood may be considered as 

 original undifferentiated embryo cells, which retain their primi- 

 tive character ; the non-nucleated red cells of the adult are the 

 mature form of nucleated cells that in the first instance are 

 colorless, and arise from a variety of tissues, and which in 

 certain diseases do not mature, but remain, as they originally 

 were at first, nucleated. When the red cells are no longer 

 fitted to discharge their functions, they are in some instances 

 taken up by amoeboid organisms (cells) of the spleen, liver, 

 etc. 



The chief function of the red corpuscles is to convey oxy- 

 gen ; of the white, to develop as required into some more diflFer- 

 entiated form of tissue, act as porters of food-material, and 

 probably to take up the work of many other kinds of cells 

 when the needs of the economy demand it. The fluid matrix 

 or plasma furnishes the lymph by which the tissues are directly 

 nourished, and serves as a means of transport for the cells of the 

 blood. 



The chemical composition of the blood is highly complex, 

 in accordance with the function it discharges as the reservoir 

 whence the varied needs of the tissues are supplied ; and the 

 immediate receptacle (together with the lymph) of the entire 

 waste of the body ; but the greater number of substances exist 

 in very minute quantities. The blood must be maintained of 

 a certain composition, varying only within narrow limits, in 

 order that neither the other tissues nor itself may suffer. 



The normal disorganization of the blood results in coagula- 



