BY BR. BURDON-SANDERSON. 185 



As soon as it escapes it coagulates. This is also an experi- 

 ment of Briicke. 



8. Recklinghausen's Experiment. A small porcelain 

 crucible is heated to redness, and allowed to cool without re- 

 moving the cover. The pericardium of a frog is then exposed 

 and divided, and a snip made in the ventricle with absolutely 

 clean scissors, the frog being held in such a position that the 

 blood discharged from the wound in the heart may be received 

 in the prepared crucible without coming in contact with the ex- 

 ternal surface of the body. The quantity of blood used should 

 not exceed ten drops. The crucible (without its cover) is then 

 placed on a ground-glass plate, and covered with a wide bell- 

 glass, the edge of which is also ground, so that it fits the glass 

 plate perfectly. The blood coagulates immediately, but during 

 the course of the next twenty-four hours it appears to become 

 liquid again. If the experiment has been carefully performed, 

 the blood remains unaltered (its colorless corpuscles retaining 

 their vital activity) for many days : it is, however, necessary 

 to renew the air contained in the bell-glass, by lifting it care- 

 fully from time to time. This experiment may be also made with 

 mammalian blood, provided that a temperature is maintained 

 equal to that of the body, for which purpose v. Recklinghausen 

 uses an air bath furnished with a Bunsen's regulator. The 

 capsule is heated to redness, because, if it were not so, the or- 

 ganic matter adherent to the surface of the porcelain would 

 determine changes in the blood, which would be fatal to the 

 vitalit} r of its elements. With a similar view every possible 

 precaution is used against other modes of contamination, 

 whether from the air or from surfaces with which the blood is 

 brought into contact. The liquefaction of the coagulum in the 

 preceding experiment is only apparent. To prove this, the 

 process must be observed microscopically under otherwise 

 similar conditions. The following method, suggested by cer- 

 tain experiments of Schlarevvski (who, however, does not appear 

 to have understood their significance), I owe to my assistant, 

 Mr. Schafer. Several very thin walled capillary tubes, not 

 more than J millimeter in diameter, are filled with blood as it 

 flows from the artery of a frog, and at once placed under the 

 No. 9 immersion objective of Hartnack. The contents of the 

 tube can be seen with perfect distinctness. At first the whole 

 of the space inclosed in the tube is occupied by colored blood 

 disks. After a few minutes it is seen that coagulation has oc- 

 curred, and that the cylindrical mass in which the corpuscles 

 are contained is separated from the glass, by a transparent 

 border in which there are no corpuscles. Next, the colorless 

 corpuscles begin to squeeze themselves out of the coagulum 

 and swim in the serum (see Fig. 192). From the activity of 

 the amoeboid movements which these corpuscles exhibit imme- 



