2 62 BIOLOGY AND HUMAN LIFE 



originated the red-and-white barber's pole, for the barber did 

 the bloodletting during a long period in European history. 



In another period of thought men tried to find a connection 

 between various natural objects, like plants or animals, and the 

 symptoms, or sights, of disease. The argument was something 

 like this : Nature made everything to be of some use to man- 

 kind ; the exact use does not always appear in every case, but by 

 careful search we should find the signs that will tell us. So a 

 plant with kidney-shaped leaves must have leaves of this shape 

 as a sign that the plant is useful in kidney trouble. The wrinkled 

 kernel of the walnut must have that pecuHar appearance, re- 

 sembling the brain, with the shell corresponding to the skull, 

 as a sign that it is useful for brain trouble, and so on. 



215. Truth in falsehood. Strange as some of these notions ap- 

 pear to us today, it is not fair for us to laugh at them. For one 

 thing, what people with queer notions think seems to them just 

 as reasonable as our thoughts do to us. For another thing, we 

 often find that there is the possibiHty of at least a small grain 

 of truth in queer notions. For example, we know today that 

 many sicknesses depend upon the presence in the body of cer- 

 tain tiny plants or animals called microbes (meaning small 

 living things), of which there are many kinds (see Chap- 

 ter XXIX). One could say today that the notion that evil 

 spirits cause disease is a true one if we only substitute mi- 

 crobes for spirits. On the other hand, these spirits cannot be 

 driven out by beating drums or burning incense or eating bitter 

 herbs. 



In a similar way, we know from modern investigations that 

 there are present in the body various juices (the internal secre- 

 tions) which have an important bearing upon health. If one is 

 in excess, we get one kind of disorder ; if another is in excess, we 

 get a different disorder. To be sure, these juices do not corre- 

 spond to the "humors" of the ancients, but they are real juices, 

 and some of them can be prepared in the laboratory and used 

 for definite changes in the body to bring about cures. We do 

 not, however, remove excess of these juices by bleeding. 



