246 



THE BLOCD. 



Fig. 80. 



RED GLOBULES OP THE BLOOD, shrunken, 

 with their margins crenated. 



of an external envelope, distinct from the parts contained within it ; 

 and although some microscopists of high authority (Kolliker, Richard- 

 son) continue to regard the existence of such a cell-membrane as proba- 

 ble, it is not generally admitted, and cannot be directly demonstrated. 



Each globule appears to con- 

 sist of a mass of organic sub- 

 stance, presenting the same 

 color, consistency, and compo- 

 sition throughout. 



The appearance of the blood- 

 globules is altered by various 

 physical and chemical reagents- 

 If a drop of blood, when placed 

 under the microscope, be not 

 protected from evaporation, the 

 globules near the edges of the 

 preparation often diminish in 

 size, becoming shrivelled and 

 crenated, presenting an appear- 

 ance as if minute granules were 

 projecting from their surfaces ; 

 an effect apparently produced 

 by the loss of a part of their 



watery ingredients. This distortion of the globules sometimes takes 

 place with great rapidity, and care is requisite not to confound a change 

 produced by external physical causes with morbid alteration of the in- 

 gredients of the blood. According to the observations of Kolliker, this, 

 as well as certain other abnormal forms presented by the blood-globules, 

 is never to be seen in the blood while circulating in the vessels. 



If water, on the other hand, be added to the blood, so as to dilute the 

 plasma, the red globules absorb it by imbibition, lose the central con- 

 cavity of their flat surfaces, assume the spherical form, and become 

 paler. If a larger quantity of water be added, it may dissolve out com- 

 pletely the coloring matter, leaving the globules as pale, colorless circles, 

 which are almost invisible on account of their tenuity. They may still, 

 however, be brought into view by the addition of an iodine solution, 

 which stains them of a yellowish color. If the water added to the 

 blood be moderate in quantity, just sufficient to be taken up by imbibi- 

 tion by the globules, but not to extract their coloring matter, a special 

 change in their form is exhibited. The edges of the globules, being 

 thicker than the central portions, and absorbing water more abun- 

 dantly, become turgid, and encroach gradually upon the central part. 

 (Fig. 81.) It is very common to see the central depression, under these 

 circumstances, disappear on one side before it is lost on the other, so 

 that the globule, as it swells up, curls over toward one side, and 

 assumes a peculiar cup-shaped form. (Fig. 81, a, a.) This figure may 

 often be seen in blood-globules after soaking for some time in the urine, 



