44 PATHFINDERS OF PHYSIOLOGY 



Change in Color of Venous to Arterial Blood. — Richard Lower, 

 1631, concluded that the change in color, venous to arterial, blood was 

 due to the exposure of the blood to the air in the lungs ; he drew the 

 further conclusion that the change in color was due not to the ex- 

 posure alone, but to the fact that the blood took up some of the air; 

 that is, according to Lower, arterial blood differed from venous in 

 that it contains air. The blood gave up its "fresh air" in the course 

 of the circulation, hence the necessity of a constant supply of fresh 

 air for the maintenance of life. **Were it not for this, we should 

 breathe as well in the most filthy prison as among the most delightful 

 pastures." * * * ^j^^ fact," he continues, "where a fire bums 

 readily there we can easily breathe." Note that there was no men- 

 tion that only a part of the air was taken up by the blood. The com- 

 mon knowledge of the time was that air was a simple substance, not 

 a mixture of several elements as we know it today. 



Mayow and His Researches. — ^The next contribution to the sub- 

 ject of respiration was that of John Mayow, bom in London in 1643. 

 Mayow was a lawyer by profession) and science was his avocation. 

 Many valued contributions to medical science were made by men 

 whose lives were spent in other callings. Priestly who discovered 

 oxygen was a Unitarian minister; Schleiden, whose name is con- 

 nected with the cell theory, was a lawyer; Schwann was a botanist; 

 Metchnikoff is a biologist. Thus many of the important discoveries 

 germain to medicine were made by men whose work was inspired by 

 the fascination of the subject in hand — ^the avocation of their leisure 

 moments. Of Mayow it was said he took his degree in law and 

 "became noted for his practice therein." Mayow's published works 

 consisted of four tracts — de sal nitro et spiritu nitro aero ; de respi- 

 ratione ; de respiratione f eotus in utero et ovo ; de motu musculari et 

 spiritibus animalibus. He showed that it was not the whole air 

 which was necessary for respiration, but only a portion, and that par- 

 ticular constituent of the air which has since become known as oxy- 

 gen. In the language of the chemists of his time, for he was essen- 

 tially a chemist, Mayow endeavors to prove "that this air which sur- 

 rounds us, and which, since by its tenuity it escapes the sharpness of 

 our eyes, seems to those who think about it to be an empty space, 

 is impregnated with a certain universal salt, of a nitro-saline nature, 

 that is to say, with a vital, fiery, and in the highest degree fermen- 

 tative spirit." The word "salt" was used by the seventeenth century 

 chemist to designate any substance not distinctly metallic or Jiquid. 



Mayow sums up the conditions necessary for combustion; "con- 

 cerning fire.it must be noted that for the ignition of this it is neces- 

 sary that igneo-aereal (evidently oxygen) particles should either pre- 

 exist in the thing to be. burnt or should be supplied from the air. 

 Gunpowder is very easily burnt by itself by reason of the igneo-aereal 

 particles existing in it. Vegetables are burnt partly by means of the 

 igneo-aereal particles existing in them, partly by help of those 

 brought to them from the air." This early chemist recognized the 

 fact that in combustion we have a chemical combination with the 

 substance burnt, and as a result an actual increase in weight. He 

 experiments with antimony, which he bums by focusing the sun's 

 rays by means of a lens; by weighing the substance he finds an in- 

 crease in weight which he attributes the "insertion into it of igneo- 



