B L O 



part of the blood be incinerated by fire, it is found to con- 

 tain much iron, which Fourcroy and Vauquelin difcovered 

 was combined with phofphoric acid in the ftate of fubphof- 

 phate of iron ; and this is the only part of the blood 

 which is found in analyfis to contain any of that metal. 

 Fourcroy examined the blood of the foetus, and fonnd that 

 the colouring' matter was darker and more abundant than in 

 the adult fubjeft. He alfo found that the blood of the 

 foetus contained no fibrine, but much more gelatine than in 

 the adult. 



The colouring matter of the blood is found, by examina- 

 tion with the microfcope, to be compofed of very minute 

 f lobular particles. Tlicy were particularly attended to by 

 .eeuwenhocck, and afterwards examined and defcribed by 

 others, chiefly by Senac, Hewfon, and Fontana. They are 

 fo fmall as fcarcely to admit of an accurate examination in 

 this climate by the common microfcope. This affertion 

 will probably be readily admitted, if it be granted that they 

 do not exceed a 200,oooth part of an iucli in diameter ; yet 

 fuch dimenfions may be Hated as the average eftimate of 

 their fize, drawn from the accounts of various obfervers. 

 Haller fays, that he faw them as large as peas by the folar 

 microfcope, and it was by tiie aid of that inllrument that 

 we are enabled to give the following account of them. A 

 drop of blood, much diluted with water, was put upon a 

 micrometer or piece of glafs, ruled by a diamond in fquares of 

 j-'^th of an inch, and put before the lens of the folar microf- 

 cope. The fquares were magnified upon the fcreen to eight 

 inches diameter. The globules of the blood were fecn un- 

 dulating to and fro in vaft numbers ; they all appeared 

 exaftly of the fame fize ; and a few which were feparated 

 from the reft were attentively examined. Thefe had all the 

 appearance of globules ; they were circular in their diflc, and 

 were regularly illumined on one fide, and (haded on the other, 

 with the prifmatic colours arranged in the middle or greateft 

 convexity ; the violet being next to the light, and the red 

 next to the (hade. On varying the focal dillance of the 

 lens, indeed, an alteration of appearance took place, fome 

 (hading appeared in the middle juft in the manner repre- 

 fented by Fontana. Upon again varying the pofition of the 

 lens, the globules appeared as at firft. Tiiis ihadowy ap- 

 pearance in the middle probably led Mr. Hewfon to fup- 

 pofe that they contained a central folid particle. It is, 

 however, generally admitted, that the colouring particles of 

 the blood are Ipherical ; and if their fize be calculated 

 from the preceding account, they will be found to be 

 lefs in diameter than the 200,000th part of an inch. 



If, for inftance, the fquare of j-^^th of an inch be magnified 

 to a fquare of eight inches, and the globules appear |th 

 of an inch in diameter, then 64 may be placed in a line 

 on one fide of the fquare, and 64 X 64 = 4096, is the 

 number that will ftand within that furface. Now, this 

 fquare is but ^^th of an inch, magnified on the fcreen to a 

 fquare of 8 inches ; then, multiply 4096 by 50, and it gives 

 204,800, as the number of thefe globules which would Hand 

 in the fquare of one inch. 



The preceding account of the blood, imperfeft as it i?, 

 yet affords us much fatisfactory information. We perceive 

 that there are contained in the blood, in a ftate of fubtile 

 fluidity, the materials of which the body is conftruftcd, and 

 which are capable of becoming folid fibres of various degrees 

 of folubility. Wi find in it alfo that aqueous liquor which 

 fills all the interlHces of the folid parts. It is true, that we 

 find in the animal body many fubllances which do not exift 

 formally in the blood, and which are new compounds of 

 matter made out of that fluid ; and for an account of which 

 the reader is referred to glandular fecretion. 



B L O 



With rcfptcl to that change which the animal matter 

 undergoes from a fluid to a folid ftate, and which is called 

 coagulation, but little is fatisfafrtorily known. It feems to 

 have been a problem amongft chemifts. Scheele attributed 

 it to the agency of caloric ; Fourcroy, to that of oxygen ; 

 and Dr. Thomfon has of late accounted for it, without fup- 

 pofing the addition of any other fubllance to the coagulated 

 matter. With reference to the lail opinion, it fhould be 

 obferved, that in coagulation, a change in the chemical pro- 

 perties of the coagulated fubftance takes place, which impHes, 

 that a chemical alteration has alfo taken place ; and that 

 even if the theory were true with refpeft to albumen, it 

 will not account for the coagulation of the fibrine of the 

 blood. Where chemiftry fails to explain phaenomena inci- 

 dent to living bodies, it is fair to inquire if life may not have 

 fome (liare in their produAion. 



Mr. Hunter thought that the coagulation of the blood 

 depended on its living powers, and fupported his opinion 

 by many ingenious arguments. To remove any obieftion 

 which miglit be made to a fluid or unorganized fubftance 

 being alive, he adverts to what happens with refpeft to the 

 yolk and wliitcof the egg, which, in confequence appirently 

 of their pofteffing a principle of life, are prefervcd from 

 putrefaftion during incubation, and which refill the efiL-fls 

 of heat and cold in a degree and manner fimilar to the lower 

 kinds of animals. His chief arguments in evidence of the 

 coagulation of the blood depending upon life are, that in 

 fome cafes where death has been caufed by lightning, or by 

 violent fatigue in running, as in animals who are hunted to 

 death, or by blows on the ftomach, the irritability of the 

 mufcles has been deftroyed, and the blood has remained 

 fluid, and never coagulated. Mr. Hunter alfo mentions, that 

 he mixed infufions of bitter vegetables, wh'ch are generally 

 confidered as tonics, with blood, and thefe did not retard its 

 coagulation, but that a folution of opium had tliat effeft. 

 As a profecutlon of this hint, the writer of the prefent 

 article caufed blood to be much diluted with water, and 

 infufions of noxious vegetables to be llirred into it ; yet in 

 thefe experiments the fibrine ilill coagulated,, and that- iu a 

 fudden manner. 



The vegetable infufions were thofe of opium, tobacco, 

 and the atropa belladonna. It may be proper to relate the 

 particulars of one of thefe experiments, in order to give a 

 general idea of the whole. Eight ounces of blood were 

 drawn from the arm into ten pints of water of 95° of 

 Fahrenheit's thermometer, containing a ftrong infufion of 

 the atropa belladonna. It was ftirred with a glafs rod ; the 

 two fluids appeared tranfparent and homogeneous. In eight 

 minutes, the temperature being 93°, a confiderable quantity 

 of floculent coagulum at once fuddenly formed, and no addi- 

 tional coagulation afterwards took place. The thermomtter 

 was attentively obferved, but no change was remarked in it 

 during this coagulation. The gentleman who performed 

 thefe experiments, wifliiug to repeat them with fome variety 

 in the mode of conducing them, obferved, however, that 

 heat was given out during the coagulation of the blood, as 

 will be feen in the following experiment. 



Ten ounces of blood were drawn into a wooden bowl, in 

 which a thermometer was held. The temperature of the 

 blood, while flowing from the vein, was 93°. In fix minutes 

 the thermometer had funk to 89", and coagulation com- 

 menced on the furface ; on elevating the bulb of the thermo- 

 meter to the coagulum on the furface, the quickfilver rofe 

 to 90 and i ; on depreffiug it to the bottom of the bowl, it 

 funk to 89. This was repeated twice with nearly the fame 

 refult, and on the third trial the quickfilver rofe to 91°; and 

 on deprefling it again, it was perceived that the blood was 

 8 coagulated 



I 



