138 KEPOHT — 1871. 



curred, or that within the pulmonary vessels considerable oxidation processes 

 of the blood contained in them had taken place. If, on the other hand, the 

 temperature of the left side were the same as that of the right side, or lower, 

 the question would still remain an open one ; for heat might be evolved in 

 the lungs, and yet the quantity might be insufficient to counterbalance the 

 loss of heat due to the evolution of large quantities of watery vapour, of car- 

 bonic acid, and to the heating of the air which we daily inspire. 



The first method, or that which consists in ascertaining the temperature 

 of the two sides of the heart, need scarcely be touched upon at present ; and 

 I shall merely confine myself to the statement that, in the hands of the most 

 experienced and reliable physiologists, and specially in those of Professor 

 Claude Bernard, it has led to the curious resxilt that the blood which 

 reaches the left ventricle is colder than that which leaves the right. This 

 result would, at first sight, appear to prove that if any heat be evolved in 

 the lungs, its amount is not sufficient to compensate the losses to which I 

 have already alluded, and rendered it absolutely essential that fresh experi- 

 ments should be conducted by a second method, which consists in ascer- 

 taining whether, when venous blood removed from the body is agitated with 

 oxygen or atmospheric aii', any changes occur in its temperature. 



The first step in the inquiry consisted in ascertaining the specific heat of 

 blood, for none of the experiments previously made had led to trustworthy 

 results. Dr. Crawford had, in the last century, advanced a theory of animal 

 heat which was based upon an assumed diff'erence in the specific heat of 

 arterial and venous blood : he supposed that the former possessed a very high, 

 and the latter a comparatively low specific heat ; so that in becoming arte- 

 rialized in the lungs, the heat resulting from the condensation, solution, and 

 probable chemical combination of oxygen with the blood became latent, 

 being, however, evolved as the blood circulated through the body, when, 

 becoming venous, it acquired a continually diminishing specific heat. Dr. 

 John Davy, in his ' Researches, Physiological and Anatomical,' vol. i. p. 141, 

 in a chapter entitled " On the Capacities of Venous and Arterial Blood for 

 Heat," described experiments which contradicted the hypothesis of Crawford 

 as to the difl^crence in the specific heat of the two varieties of blood, although 

 the extraordinary discrepancies between difi'erent experiments rendered it 

 impossible that any calculations could be based upon Dr. Davy's results. In 

 his experiments. Dr. DslXJ made use of defibrinated blood, employing for the 

 determination of specific heat the methods of mixture and rate of cooling. 



In the experiments which I performed last year, and wliich are published 

 in the last volume of the Eeports of the British Association, I made use 

 of the method of mixture, taking care to adopt aU the precautions which 

 modern experience has suggested. Making use of the perfectly fresh blood 

 of the ox, which was sometimes venous, sometimes arterial, I obtained re- 

 markably concordant results, the mean of which gave 1-02 as the coefficient 

 of the specific heat of blood. Having made this determination, I could pass 

 to the experiments intended to determine whether, in being arteriahzed, 

 blood which is perfectly venous becomes hotter. 



As a preface to my own researches on this subject, it is incumbent upon me 

 to allude to all the observations which have been made on this subject. In 

 the second volume of Dr. Davy's ' Eesearchcs, Physiological and Anatomical,' 

 at p. 168 a section is devoted to the following question: — " WJien oxygen is _ 

 absorbed by the blood, is there any production of heat ? " 



" To endeavour to determine this point," sa3^s Dr. Davy, " of so much in- 

 terest in connexion with the theory of animal heat, a very tliju vial, of the 



