BIOLOGY IN ITS WIDER ASPECTS 1219 



history of the formidable worm called Bilharzia, common in Egypt 

 and some other warm countries. The discoverer has done great 

 service to humanity, and has brought great credit to the Medical 

 School of Glasgow, where he was educated. For it is probably true 

 that if the student Leiper had not there learned and appreciated 

 the life history of the common liver-fluke, Major Leiper would not 

 have discovered the life history of bilharzia. It is a remarkable 

 fluke or trematode, peculiar in many wa3^s, e.g. in having the sexes 

 separate instead of combined, an elongated instead of a leaf-like 

 shape, and a power of entering man's body through the skin. There 

 are two common species — one preferring the intestinal region, the 

 other the renal region in man, and differing in small details. The 

 great pain which they cause is largely due to the sharp edges of the 

 microscopic eggs cutting into the walls of the blood-vessels and the 

 like. Much energy had been given to the search for the early stages 

 of bilharzia; but it was Dr. Leiper who demonstrated, during the 

 war, that the young stages lived for a while in freshwater snails 

 (like those of the liver-fluke), and that the slender fork-tailed 

 cercariae swim in the water and enter the skin of some host, such as 

 man, through lesions in the skin. We immediately understand why 

 every third child in Cairo used to be infected with bilharzia (for 

 children are fond of wading), why washerwomen and those who 

 water the gardens are much infected, and why our soldiers were 

 attacked after bathing. But Dr. Leiper did much more than remove 

 obscurities — though this is the first end of science— he showed how 

 the disease could be controlled. Thus the microscopic cercariae 

 cannot live for more than thirty-six hours in drawn water that is 

 kept quite still. 



Hook-worm and Guinea- worm. — It is probably true that one 

 of the four biggest and heaviest clouds of disease that have rested 

 on the human race is that due to hook-worm — a name given to 

 several kinds of intestinal nematodes. They cause anaemia, weakness, 

 lethargy, and despair — the "tropical depression" often deplored by 

 missionaries, colonists, and explorers. But now that we know most 

 of the story of this contemptible little worm — ^how the eggs pass 

 from man to the soil, how they develop there into sheathed and 

 unsheathed larvae, how they bore into man through the skin — there 

 is every prospect of the cloud being dispelled; and the splendid 

 work done in many parts of the world by the Rockefeller Institute 

 shows how much may be done in a short time. A recent discovery 

 indicates how the parasites can be expelled from man's body when 

 iEsculapius lifts his wand; the rest of the business presents no 

 theoretical difficulties —it means persuading the natives that certain 

 simple sanitary measures, such as the use of latrines, are life-saving. 

 Then the cloud will entirely lift. Meanwhile the use of boots saves a 

 large percentage of children from infection. 



