THE THIRD HUXLEY LECTURE 521 



different forms according to the species of the animal or its state of health. In 

 the frog the prominence of the nuclei leads to very irregular grouping of the oval 

 cells. In man the biconcave circular discs adhere under normal circumstances 

 in that position which enables their moderate degree of adhesiveness to come 

 best into play, the result being the well-known * rouleaux '. The same is seen 

 in the healthy blood of the cow. But in some animals, e.g. the horse, the 

 adhesiveness of the discs is so great that they stick to one another by the 

 parts that come first into contact, producing dense spherical masses large 

 enough to be visible to the naked eye, hke grains of red sand. These, falling 

 rapidly through the hghter plasma, leave the upper part of the liquid free from 

 red corpuscles before coagulation occurs, thus giving rise to the buffy coat, 

 whereas in the cow the delicate netw^ork of rouleaux remains suspended, and 

 no buff occurs. 



I am greatly surprised to learn that the cause of the buff}^ coat is stated 

 in some textbooks to be slowness of coagulation. Special slowness of coagu- 

 lation does not occur in bufhng blood ; nor, if it did, would it explain the pheno- 

 .menon. In whipped horse's blood the red discs aggregate into dense masses 

 as in blood freshly drawn, and falling rapidly soon leave a deep layer of serum. 

 In whipped cow's blood, rouleaux forming in the serum as in the plasma, there 

 will be found, if the animal was healthy, only a thin superficial serous layer, 

 even after a lapse of twenty-four hours. 



I once drew blood from a donkey into two similar glass vessels, one empty, 

 the other half-full of w^ater. The diluted blood and the undiluted clotted in 

 exactly the same time. But whereas in the normal blood there happened to 

 be an unusually thick layer of buff, comprising nearly two-thirds of the whole 

 mass, the watered blood gave no buff, and the microscope showed that the red 

 corpuscles had lost their natural adhesiveness. 



Human blood, as is well known, shows the buffy coat in some states of 

 inflammation. But it may also occur in anaemia.^ And it mav well make 

 our profession humble to reflect that in days within living memory bufting 

 of the clot was regarded as an indication for further withdrawal of the vital 

 fluid by venesection. 



To return from this digression : adhesiveness of the corpuscles, both red 

 and white, was seen in the vessels of an irritated area of the frog's web, as in 

 blood outside the body. But in a perfectly healthy part no such condition was 

 observed. A string tied round a frog's thigli of course made the blood in the 

 vessels of the foot motionless ; but on the slightest touch of the web the 



' In the only case of anaemia in which I examined the blood microscopically I found the red discs 

 extremely adhesive. 



LISTER u M m 



