BLOOD AND LYMPH. 



189 



small fragments. Dilute solutions of tannic acid cause the hemo- 

 globin to leave the blood-cells, and coagulate in the form of a small 

 globule at the edge of the blood-cell. In alkalies of moderate 

 strength the red blood-cells break down in a few moments. 



Besides the disc-shaped red blood-cells, every well-made prep- 

 aration shows a few small, spheric, nonnucleated cells containing 

 hemoglobin. These, however, have received as yet but little 

 attention. 



M. Bethe makes the statement that human blood and the blood of 

 mammalia contain corpuscles of different sizes, bearing a definite numerical 

 relationship to each other. " If they be classified according to their size, 

 and the percentage of each class be calculated, the result will show a 

 nearly constant proportional graphic curve varying but slightly, according 



o 



Fig. 156. Red blood-corpuscles from various vertebrate animals; X IOO (Walker's 

 model) : a, From proteus (Olm) ; b, from frog ; c, from lizard ; d, from sparrow ; e, from 

 camel ; /and^-, from man ; h, from myoxus glis ; i, from goat ; k, from musk-deer. 



to the animal species." According to M. Bethe, dry preparations of 

 human and animal blood may be distinguished from each other, with the 

 exception of the blood of the guinea-pig which presents a curve identical 

 with that of human blood. 



The red blood-cells of mammalia, excepting those of the llama 

 and camel species, are in shape and structure similar to those of 

 man. The red blood-cells of the llama and camel have the shape 

 of an ellipsoid, flattened at its short axis, but also nonnucleated. 



We have already made mention of the fact that the embryonal 

 erythrocytes are nucleated ; the question now arises as to how, in 

 the course of their development, they lose their nuclei. Three pos- 

 sibilities confront us : First, either the embryonal blood-cells are 

 destroyed and gradually replaced by previously existing nonnucle- 



