vi] Sylvias and his Pupils. 159 



fail to recognize the efforts of a man working on van Helmont's 

 lines, but attempting to shew that the fuller knowledge of 

 chemical change which he had gained by studying the actions 

 and reactions of various liquids and salts, which now dissolving, 

 now precipitating each other, now provoking, now checking 

 ebullition or effervescence, that is to say the development of 

 gas, pointed to the conclusion that it was unnecessary to take 

 refuge in subtle influences and occult agencies, but that all 

 the changes in the body were but larger and more complex 

 examples of the changes which could be produced in the 

 laboratory. 



This is pointedly shewn by what Sylvius taught concerning 

 the secretion of urine. I have already referred to Borelli's 

 mechanical theory of renal secretion. Sylvius is not content 

 with this. He says: 



" Although one may reasonably suspect that the material of 

 " the urine undergoes some special change while it is being 

 "strained through the papillae of the kidneys, it seems to me 

 "exceedingly probable at least that the blood and even the 

 " chyle is in the heart itself, through the vital effervescence 

 " which it there undergoes, prepared for the secretion of the 

 " urinary serosity, and that it is the completion only of the 

 " secretion which takes place in the kidneys." And then follow 

 these remarkable words. "Although I cannot as yet fully 

 " follow out the process, nevertheless I hope to arrive at it by 

 " the process of precipitation." 



Reading between the lines by the help of the knowledge 

 which we have gained since those days, we may find in Sylvius's 

 words a prophecy of that limitation, in which we now believe, 

 of the work of the kidney to the task of secreting, by mere 

 elimination, the urea already formed in the tissues and carried 

 to the kidney by the blood. But I quote the words also to 

 shew how complete was Sylvius's confidence in his chemical 

 methods. The change in the blood preparatory to the actual 

 work of the kidney itself, was, he had no doubt, a mere 

 chemical process, such as he might imitate in his laboratory, 

 adding one clear liquid to another, and observing how a 

 cloud of solid particles made its appearance, particles which 



