NUTRITION 37 



and (ii) the sucking phase when the blood flowing past the jaws is 

 mixed with a secretion containing hirudin which prevents the 

 blood coagulating in the crop. On the other hand, Stammers (1950) 

 found that the blood flowing from a wound made by the land leech 

 Haemadipsa had an abnormal coagulation time for some 8 minutes 

 after the leech withdrew its jaws, so presumably a certain amount 

 of hirudin was injected into the wound. It therefore seems likely 

 that an anticoagulant is produced by all blood-sucking leeches but 

 that not all of them inject this substance into the wound on the 

 host. Some at least rely on a histamine to maintain a free flow of 

 blood and use the anticoagulant to prevent the meal of blood from 

 clotting during storage in the crop. Hirudin was prepared in pure 

 form and analysed by Yanagisawa and Yokoi (1938). They showed 

 that it is an hydrolysis product of protein with an empirical 

 formula C30H60O20N8 and a molecular weight of 852. It probably 

 acts by inhibiting the thrombokinase (Lenggenhager, 1936). Only 

 0-8 mg is required to prevent indefinitely the coagulation of 5 ml 

 of rabbit blood. Lenggenhager also pointed out that one may 

 apply tincture of iodine to a leech wound without feeling any pain, 

 indicating that the saliva also has a local anaesthetic eflPect, but the 

 substance responsible has not been identified. 



It is a general character of blood-sucking leeches that they feed 

 infrequently but take large quantities of blood at one time. Hirudo 

 normally takes two to five times its own weight of blood and 

 Haemadipsa^ the land leech, may take ten times its own weight. 

 These large meals are digested slowly over a period of many 

 months. Putter (1907, 1908) drew up detailed balance sheets for 

 Hirudo. A typical example, quoted in dry weights, runs as follows : 

 a leech of 128 mg took in 640 mg during one meal. The digestion 

 of the meal took about 200 days and during that time there was 

 a loss in weight by excretion of 524 mg. The balance of 116 mg 

 had been incorporated into the tissues of the leech and as no further 

 meal was taken the leech lived on its reserves for another 100 days. 

 From this it is apparent that a leech will grow steadily if it obtains 

 a meal every six months and that it will not die of starvation if it 

 feeds only once per year. As one would expect. Putter found that the 

 leech derives most of its energy from protein breakdown so long 

 as it has blood in its crop ; he estimated the energy consumption 



