46 PATHFINDERS OF PHYSIOLOGY 



the lungs of a living animal and maintained the vital pi^ocesses by 

 means of artificial respiration, showing that the vital processes de- 

 pended upon a continual change of air in the lungs. Fracassati drew 

 attention to the fact that the red color of the upper surface of a clot 

 was due to its exposure to air. Mayow (1674) advanced the view 

 that air contained a principle capable of supporting combustion, and 

 which, absorbed in respiration, changed venous into arteral blood 

 and was the cause of heat developed in animal bodies. 



Eighteenth Century School. — Among the early eighteenth cen- 

 tury contributors to our knowledge of respiration was Stephen 

 Hales, bom 1677, who, by the way, was not connected with the med- 

 ical profession. He received his M. A. degree at Cambridge in 1703, 

 and Bachelor of Divinity in 1711. He was a clergyman by profession, 

 a calling which he followed until his death in 1761. He is chiefly 

 known as the inventor of a "ventilator," by means of which fresh air 

 was introduced into jails, mines, hospitals, and ships' holds. Four 

 years after the introduction of Hales' invention into the Savoy prison 

 only four prisoners died, whereas the mortality before its introduc- 

 tion had been as high as one hundred a year. Devoted as was Hales 

 to the church, he was even more devoted to science. He was the first 

 to determine blood pressure by actual experiment on the living animal. 



Next in chronological sequence is Joseph Black, an eminent chem- 

 ist born at Bordeaux in 1728, where his father was engaged in the 

 wine trade. Both parents were of Scotch descent. In 1746 Black en- 

 tered the University of Glasgow, where he studied chemistry under 

 Dr. Cullen. He, however, graduated from the University of Edin- 

 burg in 1754. In a graduation thesis he proved that the causticity of 

 lime and the alkalis is due to the absence of carbonic acid present in 

 limestone. He did not use the term carbondioxide but instituted the 

 term "fixed air." The former name was first used by Lavoisier in 

 1748. Black's work was a distinct contribution to chemistry. In 

 1756, he became professor of anatomy and chemistry at Glasgow, but 

 shortly become professor of the Institutes of Medicine. In the mean- 

 time he practised his profession and found opportunity for original 

 investigation. In 1766 he was transferred to a similar position in 

 Edinburgh. His lectures were noted for their clearness and what is 

 perhaps the best testimonial to any lecturer, his classes became the 

 largest and best attended in the university. Though of delicate con- 

 stitution, by constant care he lived to the fairly ripe age of seventy- 

 one. 



Black had been anticipated in his discovery of "fixed air" by Van 

 Helmont, whose researches had been made a century earlier r-Jn other 

 words, he had re=discovered the gas later to be known as C(P. By 

 using clear lime water, he was able to show that "fixed air" was given 

 off in fermentation, in expiration and that it was a product of burn- 

 ing charcoal. The chemical formula for clear lime water is Ca (OH) 2, 

 which in the presence of "fixed air," CO^, becomes Calcium Carbon- 

 at, CaCQS, which is precipitated as chalk, and water (H20). The 

 result of the chemical reaction is, of course, a reduction in the caus- 

 ticity of the original substance. " 



I quote the following extracts from his treatise on chemistry: 



"I had discovered that this particular kind of air, attracted by alkaline sub- 

 ' stances, is deadly to all animals that breathed it by the mouth and nostrils to- 



