408 



BLOOD. 



Sees to alter their form ; they are then fre- 

 quently seen to become elongated, to bend, 

 in a word, to alter their figure considerably ; 

 but they are extremely elastic, and readily and 

 soon resume their pristine state. 



Among the invertebrate animals the globules 

 of the blood are much less regular in their 

 forms. Their surface is uneven and tubercu- 

 lated, like that of a raspberry ; their contour 

 is extremely variable ; they change their figure 

 with the greatest facility, and their size 

 is considerable. In the blood of the river 

 crab for example (axtacus fluviatilis) I have 

 found their mean diameter to be 70-fgiggths 

 of a line. Several, however, were measured 

 which were no more than GTf^ths of a line 

 across, and others which were as much as 

 72 TO i 5g ths. In the oyster I have delected still 

 wider differences in the size of the globules of 

 the blood. In the same drop of this creature's 

 blood I found some globules 60 15 i g ths, others 

 only 54 TO i g ths, and some no more than 

 4 To5oo tns f a nne m diameter. 



It is well ascertained that the blood differs 

 during the earlier periods of embryotic existence 

 from what it is in after life. Messrs. Prevost 

 and Dumas have shown that the globules of 

 the blood in the chick in ovo are circular at 

 first, and only become elliptical at the period 

 when the liver is developed.* And M. Prevost 

 found that in the foetus of the goat these 

 corpuscles were at first the double in diameter 

 of those in the adult animal .f 



The structure of the globules of the blood, 

 as well as their magnitude, has been a subject 

 of great variety of opinion. The differences 

 in the conclusions, however, appear to me to 

 depend principally on the circumstances in 

 the mode of experimenting. Delia Torre and 

 Styles believed that the globules of the blood 

 were perforated in the centre and fashioned 

 like rings. When they are examined with 

 lenses of low magnifying power, they look like 

 small black points ; when viewed under an 

 instrument rather more powerful, they assume 

 the appearance of a white circle with a black 

 point in its middle ; this is evidently what has 

 given rise to the opinion we have quoted ; but 

 the appearance in question by no means de- 

 pends on the existence of a central hole in the 

 globules; it is merely the effect of the light; 

 for by using a magnifying power of 300 or 400, 

 the central point assumes the appearance of a 

 luminous spot, and by varying the position of 

 the globule, as well as the direction of the 

 rays of light, the observer may easily convince 

 himself that the globules are entire. Hewson, 

 to whom we are indebted for so many good 

 observations on the blood, was the first who 

 arrived at accurate conclusions in regard to its 

 globules. He considered them as flattened 

 vesicles, in the interior of which there is a 

 central corpuscle or nucleus. The accuracy of 

 this opinion, which has been maintained in our 



* Mem. sur le developpement du Cceur, &c. 

 Annales des Sciences Nat. 1 Serie., t. iii. 

 t Ann. des Sciences Nat. t. iv. 



own day by Messrs. Prevost and Dumas and 

 others, has been called in question by Dr. Hodg- 

 kin and Mr. Lister ; nevertheless to me it ap- 

 pears to be founded on unquestionable data. 

 In studying the blood of the Reptilia, in which 

 the globules are of very considerable magni- 

 tude, Messrs. Prevost and Dumas have even 

 seen the outer envelope of these corpuscles 

 tear, and expose the central nucleus naked. In 

 1826 I myself observed that by acting with 

 a little weak acetic acid on the globules of the 

 blood, previously placed on the object-plate 

 of a microscope, they are very speedily stripped 

 of their envelope, and their central nucleus is 

 obtained isolated.* Professor Muller,f who 

 does not appear to have been acquainted with 

 this observation of mine, has lately arrived at 

 the same conclusions, and has varied his ex- 

 periments in such wise as to place the results 

 that follow from them in the clearest possible 

 light. I shall only further add that at the 

 moment of writing this article I have again 

 assured myself of the facts as stated, by sub- 

 jecting the blood of the river-crab and that of 

 the frog to renewed examination. 



The existence of a solid, white, central 

 nucleus in the globules of the blood conse- 

 quently appears to me to be completely de- 

 monstrated ; and there is, further, every reason 

 to believe that the peripheries of these cor- 

 puscles are membranous vesicles formed of 

 the matter which gives the blood its peculiar 

 colour, or rather that they enclose this colour- 

 ing matter between their inner surfaces and the 

 central nuclei. This vesicular part of the glo- 

 bule is very elastic : whilst engaged in examin- 

 ing the capillary circulation in the lungs of 

 the water-newt, Messrs. Prevost and Dumas 

 frequently saw the globules change their figure 

 under the pressure of the moving column of 

 fluid, and mould themselves in some sort 

 upon the parts that opposed their advance, 

 but they resumed their original form the instant 

 they escaped from the influence of the unequal 

 pressure.^ In general the tegumentary vesicle 

 is collapsed upon the central corpuscle, and 

 thus forms a kind of disc of different decrees of 

 thinness near the edges, but plump or filled out 

 towards the middle. By observing the globules 

 of the blood of the frog and water-newt in diffe- 

 rent positions, the existence of this central tumi- 

 dity may be so positively ascertained as to be be- 

 yond the reach of farther doubt ; but in the hu- 

 man blood, the globules of which are extremely 

 small and almost entirely occupied by the 

 central nucleus, it is more difficult to be satis- 

 fied of its occurrence ; and Dr. Young has 

 even been led to think that these globules 

 are discs concave on both sides, an opinion 

 which has been revived and advocated anew 

 by Dr. Hodgkin and Mr. Lister. The ap- 



* Mem. sur les tissus : Ann. des Sciences Natur. 

 t. ix. 



t Observations sur 1'analyse de la Lymphe du 

 Sang, &c. Annales des Sciences Naturelles, 2 Serie, 

 Zoologie, t. i. p. 559. 



\ Vide Magendie, Physiologic, t. ii. 



