July 9, 1920] 



SCIENCE 



39 



separated into two distinct stages from tlie 

 standpoint of the changing physical properties 

 and maeroscopical appearance of the plasma 

 during the progression of clot-formation. 

 First, the fluid plasma is seen to be trans- 

 formed into a definite but transparent coagu- 

 lum of which, " on pressure between the 

 fingers, almost nothing remains." This deli- 

 cate eoagulum marks the first visible or pal- 

 pable stage in the development of the clot. On 

 standing, the transparent, almost structureless, 

 yellow eoagulum is oibserved to become gradu- 

 ally more and more turbid; until at length the 

 second stage is reached, in which the eoagu- 

 lum appears quite opaque and whitish, and as- 

 sumes the typical characteristics of a firm, 

 fibrin clot. By the use of paraffined vessels and 

 low temperature, the coagulation of human or 

 cat's blood may be delayed sufficiently to per- 

 mit centrifugalization in order to obtain a 

 clear, cell-free plasma for observation; or one 

 may study the coagulation which follows the 

 recaleification of a centrifugalized exalted 

 plasma. In either of such quickly-clotting 

 plasmas it is, of course, more difficult, but 

 nevertheless quite possible, to divide the 

 progress of coagulation into the two stages de- 

 scribed aJbove. 



The transparent-stage and the opaque-stage 

 of blood-coagulation are certainly striking 

 physical phenomena. The question accordingly 

 presents itself : Has each of these stages a sepa- 

 rate, underlying causal reaction, or do they 

 represent gradations in a continuous transfor- 

 mation of a sol into a gel ? Are the two sepa- 

 rate stages superimposable upon separate reac- 

 tions occurring between the coagulation fac- 

 tors, or does the transparency or opacity of 

 the plasma, as well as its consistency, merely 

 reflect the extent of fibrin-formation? 



It seemed that this question might find im- 

 mediate solution if it could be determined at 

 what point fibrin first makes its appearance 

 during the coagulation of a tube of plasma. 

 In comparison with the appearance of the 

 fibrin vi/hich we recognize in a firm, opaque 

 clot, certainly the transparent-stage appears to 

 be entirely fibrin-free. Now it is well known 

 that during coagulation, the formation of 



fibrin needles can be followed from the begin- 

 ning with the aid of the ultramicroscope, 

 Howell^ has described and figured this beauti- 

 ful phenomena, in which " bright specks ap- 

 pear first as short rods, which exhibit a genuine 

 saltatory movement, jumping abruptly into 

 and out of focus, and quickly fusing to form 

 longer rods and needles " of fibrin. It was at 

 the suggestion of Dr. Howell that it was de- 

 cided to use the ultramicroscope as a method 

 of approach to the solution of the question out- 

 lined above. The Siedentopf and Zsigmondy 

 slit ultramicroscope, with water-immersion ob- 

 jective was the instrument used; illumination 

 was obtained from a carbon arc-light. 



After trying various methods^ the following 

 procedure was found to yield the most satis- 

 factory results: a horse was bled from the ex- 

 ternal jugular vein through a paraffined needle 

 into a paraffined tube packed in ice. The 

 blood was taken to the laboratory, filtered 

 through a paraffined funnel surrounded by 

 an ice-jacket, and the cell-free plasma caught 

 in a second iced, paraffined tube. Plasma 

 was then, by means of a chilled paraffined 

 pipette, introduced in rapid succession into 

 (1) the cell of the ultramicroscope; (2) a 

 control cell of the same size and shape, not 

 attached to the ultramicroscope, and (3) a 

 homeopathic vial (into which i c.c. of 

 plasma was placed in each experiment). 

 These three containers could be filled within 

 ten seconds, so that coagulation began in all 

 three practically at the same moment. To 

 eliminate any error of interpretation which 

 might conceivably arise from the fact that 

 one vessel was filled a few seconds before 

 another, the order in which they were filled was 

 varied in different experiments. There was, 

 however, no evidence indicating that this theo- 

 retical source of error had the slightest influ- 

 ence upon the results in any experiment. 



The rationale of using three plasma con- 

 tainers in these experiments may be here ex- 

 plained: (1) The cell of the ultramicroscope 

 was observed closely after filling, in order to 

 determine the time of appearance of the earliest 

 visible needles of fibrin; (2) the homeopathic 



3 Howell, Am. Jour. Thys., 1914, XXXV., 143. 



