PREVIOUS INVESTIGATIONS. 11 



1789. Almost simultaneously with Lavoisier's paper we 

 have an interesting communication from Jurine of Geneva. In his 

 researches Jurine employed a Fontana eudiometer, then much used 

 in Europe as the earliest method for analyzing gases, particularly 

 atmospheric air. With this apparatus he studied the influence upon 

 the expired air of various physiological processes, among others those 

 of the ingestion of food. 1 The experiments were confined exclusively 

 to determinations of the differences in composition of the expired air. 

 The subject evidently breathed through a glass tube flattened to fit 

 the shape of the mouth, and the expired air was collected at times over 

 water and at times over mercury in a bell-jar. A stopcock was turned 

 at the beginning and end of each expiration. Among other experi- 

 ments, Jurine made three on the influence of food upon the respiratory 

 exchange as shown by the changes in the composition of the air. Both 

 a fasting experiment and a food experiment were made with each of 

 three subjects, a young girl 10 years old, a man 36 years old, and a 

 woman 62 years old. The food experiments were to determine if the 

 increased blood circulation, depending on or incident to digestion, 

 would increase the oxygen consumption. In the air collected over 

 water no change was found in the oxygen content, while in the air 

 collected over mercury a very sensible increase was found in the pro- 

 portion of carbon dioxide present. The total amount of carbon dioxide 

 produced in 24 hours was computed by Jurine from the average number 

 of respirations and from the volume expired per respiration. We find 

 no evidence, however, that he calculated the total increase in the carbon- 

 dioxide production due to digestion. 



This method of studying the expired air was followed for a number 

 of years by other scientists, little emphasis being placed upon the total 

 quantitative amount of carbon dioxide expired in a given time, but 

 chiefly upon the alteration in the carbon-dioxide content of the expired 

 air. We know now that this change in composition has but little sig- 

 nificance unless accompanied by some knowledge of the total ventila- 

 tion of the lungs, a factor that was entirely overlooked, or at least 

 undetermined, in many of the early researches. 



Prout, 1813. One of the most extended observations upon the influ- 

 ence of food on the carbon-dioxide percentage of the expired air is 

 that recorded by Prout. 2 The subject, Prout himself, expired into a 

 bladder, regulating the number of expirations to six. A sample of air 

 was then taken in a tube and the carbon dioxide was determined by 

 absorption with strong caustic potash. Prout remarks that as his 

 main object was to discover general laws he did not pay so much 

 attention to the question of the influence of food, although during the 

 three weeks of experimentation he ate only the simplest food and with 



'Jurine, Histoire et M6m. Soc. Med., 1789, 10, p. 19. 

 'Prout, Annals of Philosophy, 1813, 2d ed., 2, p. 328. 



