SERVETUS 33 



veins. They thus mutually give to each other blood and 

 spirit through certain invisible and extremely narrow 

 passages." The sentence presumably means that these 

 fine passages unite artery and vein in the lung no less 

 than in other parts of the body. 



There is, however, in Galen nothing about circulation , 

 the essence of which is movement alwavs in the same 



J 



direction. On the contrary, Galen emphasises the 

 mutual character of the exchange and of the movement. 

 Servetus, however, seizes on the passage and boldly 

 declares that ' ' the vital spirit passes from the arteries to 

 the veins through the anastomoses" It is a very inter- 

 esting illustration of how small a thing, a hint, an excep- 

 tional use of a word, a strained analogy, may lead to 

 a great discovery. It is also a remarkable illustration 

 of how near a great discovery a man may be without 

 making it. Servetus was on the very brink of such a 

 discovery ; indeed, he actually enunciates it, as we shall 

 immediately see. But he passes it by, deaf and blind to 

 everything save the course of his own theological argu- 

 ment. The one passage, the one idea, in his book that 

 time has shown to have been really original and important 

 he introduces as an incident in the course of his argument. 



He tells us that he considers that blood and life or 

 spirit are the same in the sense that the one contains 

 or includes the other. He then explains that to under- 

 stand this we must learn how the spirit is generated 

 and produced in the blood. In the course of explaining 

 the process, he gives a perfectly clear exposition of the 

 lesser circulation. He no longer attributes the genera- 

 tion of spirit entirely to the heart, but rather to the lungs. 



The vital spirit," he says, " is generated through the 



mingling in the lungs of the inspired air with the subtle 



blood which is communicated to it from the right ventricle 



to the left. This communication does not, however, 



3 



