THE LEECHES OF MINNESOTA 7 



countries. One American leech farm sold as many as 1000 or more 

 a day. Today leeches are so seldom used that few young people 

 have seen a medicinal leech, and most physicians of today do not 

 know how to apply a leech properly. It is difficult to say how 

 much leeches are still used because the leech industry has ceasd 

 to be one of commercial importance. That they are, in comparison 

 with former days, used very seldom is evident from the fact that 

 where several thousand were employd fifty years ago there is 

 scarcely one employd today. It has been estimated that France 

 used about twenty five million in 1846. About 7 million were used 

 in the London hospitals in 1863 and five to six million in the 

 hospitals of Paris. Today one can not find a leech in most of our 

 hospitals. Naturally the price of the medicinal leech has dropt. 

 About eighty years ago medicinal leeches were worth $50.OO-$75.0O 

 per thousand. About fifty years ago they were worth $20.00-$40.00 

 per thousand and today they are not worth more than $20.00 per 

 thousand with a very much restricted market. 



Hirudo medicinalis, the medicinal leech, included a number of varieties 

 that up to about the middle of the nineteenth century were almost univer- 

 sally used by the medical profession. When full grown and extended this 

 leech is from eight to twelve inches long and about half an inch wide. The 

 general or ground color is a dull yellowish brown to gray or greenish gray. 

 On each side there may be an orange stripe borderd with black and, as a 

 rule, the dorsal side is markt with six rust-red longitudinal lines spotted with 

 black. The coloring, however, varies so much that at least sixty-four 

 varieties basd on these minor differences have been describd. Among 

 the most prominent of these are the socald German and Hungarian medi- 

 cinal leeches. The German medicinal leech (H. medicinalis) is markt on 

 the dorsal side with six longitudinal reddish lines and on the ventral side 

 with black spots. The ventral side, however, varies from the spotted to 

 an almost uniformly black coloring. This variety is the common one in 

 the markets of Germany, France, Denmark, Sweden, Russia, England and 

 America. The Hungarian variety is markt with only four reddish to brown- 

 ish lines on the dorsal side and an unspotted olive green on the ventral 

 side. This variety is found most common in southern and southeastern 

 Europe. 



The medicinal leech (of all varieties) prefers lakes and ponds having 

 a clay bottom and a rich growth of plants. It swims about actively dur- 

 ing the daytime and during its earlier years feeds largely on the blood of 

 some of the socald coldblooded animals, like turtles and fish. When 

 mature it feeds on the blood of socald warmblooded vertebrates. 



The eggs are enclosd in oval coccoons about an inch long. The 

 coccoons are deposited in the earth near the shore during June, July and 

 August. The young come out six to eight weeks after the eggs are laid 

 and do not become fullgrown until rive years later. They are not of any 

 value for bloodletting until three years old. Under favorable conditions 

 they may live for more than twenty years. 



When bloodletting was an almost universal practis various 

 means were employd to make gorgd leeches disgorge the blood 



