108 MANUAL OF HISTOLOGY. 



colourless fluid, the plasma, or liquor sanguinis, in which two kinds of 



cells are suspended, namely, the " red blood-cells " and the " colourless," or 



"lymph-corpuscles" of the blood (lymphoid-cells) (fig. 110). The first occur 



^-v x-^-y^v i n g rea * preponderance, and are the cause of the 



(EJ > re( ^ c l ur f the blood, while the latter generally 



' represent but a small fraction of the number of 



jj $@b~d ce ^ s contained in the whole mass of the fluid in 



. Jj /->. question. Besides these, we also meet in human 



(ff) a blood with conglomerationsof minute pale granules, 



Fig. no.-Human Wood-ceils, measuring 0-001 1-0-0022 mm. (Schultze). 



From above, a a; half side The coloured Uood-cells discovered long ago by 



view, b; seen completely * . t ji-ii ,1 j 



from the side, c; lymph- Malpigtii, and which have since then received very 

 corpuscles, d. difi ? erent names, such as " blood-granules," " blood 



globules," " blood-disks," "blood-corpuscles," and " blood-vesicles," appear 

 in human blood as circular formations, with a yellowish tint, and sharp 

 and delicate contour. They display among themselves but little variety 

 either in size or otherwise. Their number in a drop of blood is enormous; 

 it may be accepted as being about five millions to the cubic millimeter. 

 C. Schmidt estimates their specific gravity at 1-088-1-089, Welcker at 

 1*105. The diameter of the cell in the blood of the male averages 

 0-0077 mm., with extremes of from 0-0039 to 0-0024 mm. 



With very accurate focus the living blood-corpuscles lying in the plasma 

 present in their centre a clear colourless space, and also at a spot in their 

 interior a slight shading of more or less semicircular outline, situated at 

 that side of their border opposite to that from which the light is thrown 

 on the field (fig. Ill, a). 



The reason of this appearance becomes clear so soon as the cells are set 

 in motion. Far from preserving their circular form, in rolling over the 

 glass plate of the microscope, they appear when standing on their edge 

 (c c) like thin biscuit-shaped rods, with thickened bevelled ends, and con- 

 striction in the middle. In thickness they are about O'OOIS mm. 



From what we have just seen, there can be hardly any doubt that the 

 form of the cell is in reality that of a biconcave disk with bevelled, 

 swollen edges. The volume of the human blood-corpuscle has been 

 estimated by Welcker to be 0*000000072 cub. millim, the weight 0-00008 

 milligram, and the superficial extent 0-000128 square millim. Its body is 

 composed of a completely homogeneous substance of a yellowish colour 

 by transmitted light ; this deepens to a rather reddish tint at points where 

 any two cells overlap one another. Should they commence to form 

 larger aggregations, they then begin to show the red colour of the blood 

 itself. 



67. 



In order to make ourselves better acquainted with the further nature 

 of the blood-corpuscle, it is necessary to observe the effects of certain 

 external agencies upon it. If we expose a drop of blood on the glass 

 plate of the microscope for a short time uncovered, and allow it to evapor- 

 ate, the form of the cell changes (fig. Ill, b). With a decrease in size 

 down to from 0*0059 to 0-0052 mm., it becomes irregularly angular, 

 lumpy, and frequently stellate, the pointed portions coming out as dark 

 dots in the object. We have here to deal with a shrinking together of 

 the body of the cell depending on a loss of water, a process the interpreta- 

 tion of which in human blood presents many difficulties owing to the 



