THE BLOOD. 165 
nucleated, etc. Again, the white cells may be so multiplied that 
the blood may bear in extreme cases a resemblance to milk. 
Jn these cases there has been found associated an unusual 
condition of the bone-marrow, the lymphatic glands, the spleen, 
and, some have thought, of other parts. 
The excessive action of these organs results in the production 
and discharge into the blood-current of cells that are immature 
and embryonic in character. This seems to us an example of 
a reversion to an earlier condition. Itisinstructive also in that 
the facts point to a possible seat of origin of the cells in the 
adult, and, taken in connection with other facts, we may say, to 
their normal source. These blood-producing organs, having 
too much to do in disease, do their work badly—it is incom- 
plete. 
Although the evidence, from experiment, to show that the 
nervous system in mammals, 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 anemia 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 amceboid 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 differ- 
entiated form of tissue, act as porters of food-material, and’ 
