16 THE ESSENTIALS OF HISTOLOGY. 



blood. 1 The mixing of human blood with the blood or serum of various 

 animals also has a similar action, probably owing to differences of 

 density or alkalinity. Tannic acid produces a peculiar effect (fig. 14, g); 

 the haemoglobin is discharged from the corpuscle, but is immediately 

 altered and precipitated, remaining adherent to the envelope in the 

 form of a round or irregular globule of a brownish tinge (hematin ?). 



Some of these reactions occur by process of osmosis as in the case of water, 

 but in others a physical or chemical solution of the envelope of the corpuscle 

 is produced, and the haemoglobin is thus allowed to escape. The film or 

 envelope is probably in large measure composed of lecithin and cholesterin 

 (along with a little cell-globulin Halliburton), and these are substances 

 which possess many of the physical properties of fats, although of a different 

 chemical composition. If we assume this to be its composition the running 

 of the red disks into rouleaux can readily be explained, since it has been 

 shown by Norris that disks of any material, e.g. cork, floating in a fluid, tend 

 in the same way to adhere in rouleaux, provided their surfaces are covered 

 with a layer which is not wetted by the fluid. 



The envelope of the red corpuscle is often termed the stroma (Eollett), but 

 this name rests upon an entirely false conception of the structure of the cor- 

 puscle, and although of late years almost universally used, it ought to be 

 entirely abandoned. In adopting the name, it was supposed that the corpuscle 

 is formed of a homogeneous porous material (stroma), in the pores of which 

 the haemoglobin is contained, but there is no reasonable foundation for this 

 belief, whereas the supposition that there exists a delicate external film or 

 envelope inclosing a coloured fluid is in accordance with all the known facts 

 regarding the action of reagents upon these bodies. 



The structure of the colourless corpuscles is also brought out by 

 the action of some of these reagents. As the water reaches them their 

 amoeboid movements cease ; they become swollen out into a globular 



FIG. 15. 



1. first effect of the action of water upon a white blood corpuscle: 2, 3, white corpuscles 

 treated with dilute acetic acid ; n, nucleus. 



form by imbibition of fluid (fig. 15, 1), and the granules within the 

 protoplasm can be seen to be in active Brownian motion. Their nuclei 

 also become clear and globular, and are more conspicuous than before. 



1 In the blood of some animals crystals of haemoglobin readily form after its 

 separation by any of these means from the red corpuscles. These crystals are 

 rhombic prisms in most animals, but tetrahedra in the guinea-pig, and hexagonal 

 plates in the squirrel. They are most appropriately studied along with the 

 chemical and physical properties of blood, and are therefore omitted here. The 

 same remark applies to the minute dark-brown rhombic crystals (hcemin), which 

 are found when dried blood is heated with glacial acetic acid, and to the reddish- 

 yellow crystals of hcematoiditt, which are found in old blood extravasations. 



