482 Prof. J. B. Haycraft. On the Action of a [Apr. 3, 



white corpuscles is not destroyed, and that the formation of rouleaux 

 by the red disks is not necessarily a phenomenon of coagulation. 

 The coagulation of the perivisceral fluid of the sea urchin is, accor- 

 ding to the observations of my friend Mr. Patrick Geddes. not due to 

 the intercellular formation of fibrin in the plasma, but to active 

 amaeboid movements of the white corpuscles. The pseudopodia of 

 neighbouring cells join, become welded together, and contract so that 

 all the cells are massed together into a solid clot. Professor Schafer 

 maintains that there is also a formation of fibrin in the ordinary way 

 which has been overlooked by Mr. Geddes.* I have not examined 

 this fluid myself, and do not feel qualified to speak upon this subject ; 

 but certainly the blood of crabs, crayfish, and lobsters clots in the 

 way described by the former of these authors, there being no inter- 

 cellular formation of fibrin. In this case, then, the leech extract 

 will probably not prevent coagulation. The blood of a crayfish was 

 mixed with one-third of its volume of leech extract. A drop was 

 examined microscopically at the ordinary temperature. The cells 

 exhibited normal ameeboid movements, and coagulation was appa- 

 rently quite normal. 



Heretofore we have spoken of the extract of leech gullet and 

 buccal cavity, but it has not yet been shown which is the source of 

 this excretion. All that can be said is that it comes from either the 

 gullet or mouth and sucker of the animal. Careful microscopical 

 preparations were made of the anterior half of the leech, to seek for 

 glandular structures. The animals were hardened for ten hours in 

 saturated picric acid solution, and longitudinal mesial sections were 

 made with a freezing microtome. The sections were stained with 

 picrocarmine. No signs of ordinary glandular structures were to be 

 observed either opening into the sucker, or into the alimentary canal. 

 Some of the epithelial cells forming the integument of the leech are 

 much elongated, passing down even among the subjacent muscular 

 fibres. These have been looked upon as unicellular glands (Ray- 

 Lankester), and in the sucker one may see small collections of these. 

 If the skin lining the sucker be removed, it is found to be active in 

 preventing coagulation. Not in a less degree however is the anterior 

 part of a leech from which the skin of the sucker has been removed. 

 Probably then the secretion is derived from the epithelial cells lining 

 the sucker and buccal cavity ; it may be that the unicellular glands 

 of the sucker share in its production. 



The products of the digestion of albumin by pepsin have an im- 

 portant action in retarding coagulation. Dr. Schmidt-Mulheim,f 

 working under the direction of Professor Ludwig, has shown that 

 blood received from an open vein into a solution of peptone does not 



* " Proc. Koy. Soc," vol. 34, p. 370. 



f " Archiv. fur Phys. : " Du Bois-Keymond, 1880, p. 33. 



