PROPERTIES OF THE BLOOD. 429 



572. The form of the Red Corpuscles is not unfrequently seen to change 

 during their circulation ; but this is generally in consequence of pressure, from 

 the effects of which, however, they quickly recover themselves. In the narrow 

 capillary vessels, they sometimes become suddenly elongated, twisted, or bent, 

 through a narrowing of the channel ; and this may take place to such a degree 

 as to enable the disc to pass through an aperture which appears very minute 

 in proportion to its diameter.* When undergoing spontaneous decomposition, 

 the blood-discs become granulated, and sometimes (as long ago noticed by 

 Hewson),even mulberry-shaped ; and particles in which these changes appear 

 to be commencing may be found in the blood at all times. It has been ascer- 

 tained that bile and urea exert a peculiar solvent power on the blood-corpuscles ; 

 and hence we can understand one of the modes in which a retention of these 

 substances in the circulating fluid ( 649) proves so injurious. The size of the 

 blood-discs is liable to considerable variation, even in the same individual ; and 

 this is at once understood when they are considered as cells in different stages 

 of growth. There are, however, limits to this variation for each species ; and 

 the blood-discs of one tribe of Mammalia can rarely be confounded with those 

 of another. The diameter of the corpuscles bears no constant relation to the 

 size of the animal, even within the limits of the same class ; thus, although 

 those of the elephant are the largest among Mammalia (as far as is hitherto 

 known), those of the Mouse tribe are far from being the smallest, being in fact 

 more than three times the diameter of those of the Musk Deer, there is, 

 however, a more uniform relation between the size of the animal and that of 

 its blood-discs, when the comparison is made within the limits of the same 

 order. In man, the diameter varies from about l-4000th to l-2800th of an 

 inch ; the average diameter is probably about 1 -3400th. 



a. The following measurements of the blood-discs of various animals, are chiefly 

 given on the authority of Mr. Gulliver. The diameter of the corpuscles in the Quad- 

 rumana is generally about the same with that of the Human blood-discs; there is, how- 

 ever, a slight diminution among the Lemurs, and there is more variation among them, 

 than among the Monkeys. Among the Cheiroptera, the diameter of the corpuscles is 

 somewhat less than in the preceding order, the average being about l-4300th of an inch. 

 The blood-discs of the Mole are still smaller, averaging only the l-4750th of an inch; 

 those of the Hedge-hog, however, are larger, being about l-4100th. Among the Planti- 

 grade Carnivora, the average is about l-3800th, and from this none depart very widely: 

 but among the Digitigrade species there is a considerable range; in the Weasel tribe, 

 the average is about l-4800th ; in the Feline, it is about l-4400th ; in the Dog tribe,f there 

 is a range of averages from l-3400th to l-4100th ; and in the Seal, the average is about 

 l-3300th. Observations on the blood-discs of the Cetacea are much required. Among 

 the Pachyderrnata, the average, excluding the Elephant (the diameter of whose blood- 

 same degree. The nucleus is clearly seen to consist of a number of moderately-bright 

 spherical granules, of which from 20 10 30 could be seen in one plane or focus, the total 

 number being of course much greater. When removed from the capsule, the nuclei are 

 colourless, and the component granules have a high refracting power. Viewed in situ, 

 they present a tinge of colour lighter than that of the surrounding fluid, and dependent 

 upon the thin layer of that fluid interposed between the nucleus and the capsule. As the 

 fluid contents of the blood-disc in part evaporate during the process of desiccation, the 

 capsule falls into folds in the interspace between the nucleus and the outer margin; these 

 folds generally take the direction of straight lines, three to seven in number, radiating 

 from the nucleus. 



* " Blood-corpuscles are repeatedly found, quite unaltered in appearance, on the mucous 

 surfaces, when no solution of continuity whatever can be detected in the vessels." Gul- 

 liver, in Gerb. Gen. Anat., p. 78. 



f Two facts of much interest in Zoology have been brought to light by Mr. Gulliver's 

 examination of the diameter of the blood-corpuscles of this tribe. The difference between 

 those of the Dog and Wolf is not greater than that which exists among the varieties of 

 the Dog, whilst the discs of the Fox are much smaller. The discs of the Hyaena are far 

 more approximate to those of the Canidae than they are to those of the Felidae. 



