1220 LIFE : OUTLINES OF GENERAL BIOLOGY 



Take another illustration which shows how zoological under- 

 standing may count. For thousands of years there has been some 

 knowledge of the guinea-worm, the female of which lies coiled, one 

 to six feet in length, below the human skin, and produces abscesses 

 and ugly sores. The male usually remains hidden. This guinea-worm 

 was probably the Fiery Serpent that bit the children of Israel trek- 

 king in the desert. It enters man, as Major List on showed, through 

 drinking water containing a Cyclops — a common water-flea, which 

 harbours the juvenile stages. But our point at present concerns its 

 exit. It used to be coaxed out by winding it patiently round a strip 

 of wood, turned a little day after day. Perhaps Moses' coiling serpent 

 was not simply a symbol of hope, but a diagrammatic object-lesson 

 of treatment for his afflicted people. For as one "learned in all the 

 wisdom of the Egyptians", he must have studied medicine in course 

 of this, as indeed the Mosaic Law shows at various points. Nowa- 

 days, however, the patient sits for hours with his leg or arm in 

 water, and the long female comes out of herself. The modern method 

 follows from an understanding of the zoological fact that the mature 

 female should emerge from the host to lay eggs in the water. The 

 needed preventive treatment is to take care of the outside of the 

 water-vessel, to cleanse the well from time to time, and to keep a 

 good parapet round it; all to abate the otherwise constant intro- 

 duction of eggs for the Cyclops to swallow. 



Protozoology. — One of the characteristic features in the 

 twentieth-century zoology and medicine has been the development 

 of protozoology. Its origins go far back, but in the last quarter of 

 a century it has grown with such rapidity that outside the ranks 

 of the experts few are keeping in pace with its details. It has its 

 laboratories and professors and journals; and of the two first, at 

 least, we need more. What exactly is the change? It is the dis- 

 covery that many microscopic animals are just as important as 

 many of the bacteria. Thus, it is well known that Protozoa are 

 responsible for malaria and sleeping sickness ; and it is perhaps more 

 impressive not to continue the list, as we might. 



Speaking of microbes leads one to think of phagocytes — our 

 natural bodyguard of amoeboid cells — and it must be remembered 

 that Metchnikoff was first of all a zoologist. This is discussed under 

 Phagocytosis, but we wish to make the point that the early chapters 

 in the history of the doctrine of phagocytosis were zoological, 

 beginning as far back as 1862, when Haeckel observed that minute 

 grains of indigo injected into the mollusc Thet3^s were engulfed by 

 amoeboid cells. 



Medical Entomology. — We cannot think of the development of 

 protozoology without recognising the correlated development of 

 medical entomology; for there has been great insight into the part 

 played by some insects, and likewise some ticks and mites, as 



