130 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 



portion at the same time separating in some degree from the central part. The blood-cor- 

 puscle, in this stage of development, has the appearance of a slightly flattened round cell, 

 formed of a somewhat delicate but elastic membrane, with a nucleus in the centre. At this 

 time a number of these bodies, being close together in the Held, presents a yellowish colour. 

 The cell is disc-like, rather concave, but the nucleus convex. In the third stage, one side of 

 the corpuscle gradually elongates, giving it a pear-shaped appearance ; the opposite side then 

 elongates itself in a similar manner, and to the same degree. The concavity between the 

 nucleus and border disappears, and the whole becomes slightly convex. The hue at the 

 same time gradually becomes redder."* 



The corpuscles are generally larger in the embryo than in the adult, espe- 

 cially soon after the period of their first formation; it was remarked by M. 

 Prevost, that in the fetal goat they were at first twice the size of those of the 

 mother. Mr. Gulliver has observed, however, that at a later period of utero- 

 gestation they are sometimes smaller than the average dimension of the adult ; 

 but perhaps all such observations are to be received with hesitation, owing to 

 the fact mentioned by him, that the variety in the magnitude of the fetal cor- 

 puscles is much greater than in the full-grown animal. 



150. In regard to the uses of the Red corpuscles of the Blood, in the Ani- 

 mal economy, it appears to the Author that a definite conclusion may be now 

 arrived at. Their existence in the circulating fluid is nearly confined to the 

 Vertebrated classes ; the corpuscles which are seen in the blood of the Inver- 

 tebrated, being mostly analogous rather to the Colourless corpuscles, presently 

 to be described as present in the blood of the higher animals. Among the 

 lower Invertebrata, indeed, the Red corpuscles seem to be altogether wanting; 

 and the same may be said of the embryos of the highest animals, at an early 

 period of their development ; as well as of the early state of parts that are 

 being newly formed, at any period of their lives. Hence the inference ap- 

 pears highly probable, that they are not essentially necessary to the produc- 

 tion of the organizable elements of the blood, or of the organized tissues ; in 

 other words, to the simple acts of growth and nutrition. The Red corpuscles 

 are most abundant in those classes among Vertebrata, which maintain the 

 highest temperature ; thus, they are somewhat more numerous, in proportion 

 to the whole bulk of the Blood, in Birds than in Mammalia ; and far more in 

 the latter, than in Reptiles and Fishes. As it is evident that they undergo 

 very important changes in the pulmonary and systemic capillaries, their co- 

 lour being changed from purple to red in the former, and from red to purple 

 in the latter, it seems highly probable that they have as their principal office, 

 the introduction of oxygen into the blood that circulates through the systemic 

 capillaries, and the removal of the carbonic acid set free there ; serving, in 

 fact, as the medium for bringing the tissues into relation with the air, the in- 

 fluence of which is necessary for the maintenance of their vital activity. In 

 the Invertebrata generally, whose respiration is very feeble, this end will be 

 sufficiently answered by the fluid plasma of the blood ; the alterations in which, 

 under the influence of the air, have been already noticed ( 115, 116 ). And 

 in Insects, the only class whose respiration is at all active, we find the air 

 directly conveyed into the tissues ; the circulating fluid not being employed as 

 its carrier ( 18). We shall hereafter find, that the influence of oxygen upon 

 the Nervous and Muscular systems is essential to their vital activity ; and it 

 seems to be by their agency in bringing these into relation, that the Red cor- 

 puscles possess that intimate connection with the Animal functions, which we 

 find them to possess. The animals whose temperature is the highest, are 

 also those whose senses are most acute, and whose movements are most ener- 

 getic : whilst, on the other hand, if there be any unusual diminution in the 



* London and Edinburgh Monthly Journal, September, 1842. 



