1 86 Letters 



attain to the hidden things of truth when we take the 

 averments of our senses as the guide which God has 

 given us for attaining to a knowledge of his works ; 

 avoiding that specious path on which the eyesight 

 is dazzled with the brilliancy of mere reasoning, and so 

 many are led to wrong conclusions, to probabilities 

 only, and too frequently to sophistical conjectures on 

 things ! 



I further congratulate myself on his confirmation of 

 my views of the circulation of the blood by such lucid 

 experiments and clear reasons. I only wish he had 

 observed that the heart has three kinds of motion, 

 namely, the systole, in which the organ contracts and 

 expels the blood contained in its cavities, and next, 

 a movement, the opposite of the former one, in which 

 the fibres of the heart appropriated to motion are 

 relaxed. Now these two motions inhere in the sub- 

 stance of the heart itself, just as they do in all other 

 muscles. The remaining motion is the diastole, in 

 which the heart is distended by the blood impelled 

 from the auricles into the ventricles ; and the ventricles, 

 thus replete and distended, are stimulated to con- 

 traction, and this motion always precedes the systole, 

 which follows immediately afterwards. 



With regard to the lacteal veins discovered by Aselli, 

 and by the further diligence of Pecquet, who discovered 

 the receptacle or reservoir of the chyle, and traced the 

 canals thence to the subclavian veins, I shall tell you 

 freely, since you ask me what I think of them. I had 

 already, in the course of my dissections, I venture 

 to say even before Aselli had published his book, 1 

 observed these white canals, and plenty of milk in 

 various parts of the body, especially in the glands of 

 younger animals, as in the mesentery, where glands 

 abound ; and thence I thought came the pleasant 

 taste of the thymus in the calf and lamb, which, as 

 you know, is called the sweetbread in our vernacular 



1 Published at Milan in 1622. 



