418 



THE BLOOD. 



[CH. XXVI. 



Heat. The effect of heat up to 50 60 C. (120 140 F.) is to cause the 

 formation of a number of bud-like processes (fig. 349). 



Electricity causes the red blood-corpuscles to become 

 crenated, and at length mulberry-like. Finally they re- 

 j cover their round form and become quite pale. 



Fig. 349. Effect of 

 heat. 



The Colourless Corpuscles. In human blood 

 the white or colourless corpuscles or leucocytes 

 (when at rest) are nearly spherical masses of granu- 

 lar protoplasm. In all cases one or more nuclei exist in each 

 corpuscle. The size of the corpuscles varies considerably, but 

 averages 25 1 00 of an inch (lo/x) in diameter. 



In health, the proportion of white to red corpuscles, which, 

 taking an average, is about i to 500 or 600, varies considerably 

 even in the course of the same day. The variations appear to 

 depend chiefly on the amount and probably also on the kind of 

 food taken ; the number of leucocytes is generally increased by a 

 meal, and diminished by fasting. Also in young persons, during 

 pregnancy, and after great loss of blood, there is a larger pro- 

 portion of colourless blood-corpuscles. In old age, on the other 

 hand, their proportion is diminished. 



Varieties. The colourless corpuscles present greater diversities 

 of form than the red ones. Two chief varieties 

 are to be seen in human blood ; one of which 

 contains a considerable number of coarse gran- 

 ules, and the other, which is paler and less 

 granular, contains several nuclei united by fine 

 threads of chromatin. 



The granules of these cells have an affinity 

 for acid, aniline dyes like eosin. They are there- 

 fore spoken of as oxyphile or eosinophile. The 

 large granules of the coarsely granular cells are 

 much more deeply stained by eosin than the 

 granules of the finely granular cells. The latter 

 cells are by far the most numerous ; the coarsely 

 granular cells only comprise about 5 per cent, 

 of the total number of leucocytes. In size the 

 variations are great, for in most specimens of 

 blood it is possible to make out, in addition to 

 the full-sized varieties, a number of smaller cor- 

 puscles, consisting of a large spherical nucleus 

 surrounded by a variable amount of more or 

 less granular protoplasm. These small corpus- 

 cles are the undeveloped forms of the others, and are derived 

 from the cells of the lymphatic glands ; they are called lympho- 



Fig. 350. A. Three 

 coloured blood- 

 corpuscles. B. 

 Three colourless 

 blood - corpuscles 

 acted on by acetic 

 acid ; the nuclei 

 are very clearly 

 visible Human 

 blood. X 900. 



