INTERNAL RESPIRATION 553 



be expressed as 100, the relative powers of other tissues would be, 

 liver 81-47, involuntary muscle 72-4, and mucous membrane of 

 the stomach 57-05. The lungs had a very feeble power of re- 

 duction, and in this respect Bernstein's results show an interesting 

 difference from those of Ehrlich. 1 If a frog's heart be supplied 

 with solutions of fresh blood, the reduction of the oxy-haemoglobin 

 can be determined with the spectroscope ; working with this 

 method, Yeo found that the heart during contraction reduces 

 the solution about ten times as quickly as when it is at rest. 



There is, however, one criticism which is effective against all 

 such experiments upon surviving tissues ; there is no circulation 

 of blood to carry oxygen to, and remove carbon dioxide from, 

 the cells which lie in the deeper parts of the organ ; diffusion will 

 only occur readily at the surfaces of exposure. This abnormal 

 condition, especially the lack of oxygen, will result in disordered 

 metabolism. This difficulty is to a certain extent overcome by 

 the method introduced by Ludwig ; an artificial circulation of 

 blood is maintained, and the gaseous or other changes in the blood 

 are determined. The results so obtained, however interesting 

 they may be, cannot be considered normal, for the organ has been 

 removed from the control of the central nervous system and from 

 the influence of that interaction of organs which is so well 

 demonstrated by the " internal secretions " : the organ may be 

 said to be in a living condition, or with more truth, perhaps, in a 

 living death ; but the chemical changes exhibited cannot be con- 

 sidered to represent truly the condition in the intact organ within 

 the body of a living animal. The blood used for the artificial cir- 

 culation must be deprived of its power of coagulation, and many 

 of the means employed for this purpose are known to alter the 

 nature of the blood as a respiratory medium. The respiratory ex- 

 change of an excised mass of muscles, such as those of a limb, rises 

 and falls with the external temperature ; a similar group of muscles 

 in an inact mammal would be influenced by the nervous regulation 

 of temperature, when the animal was exposed to changes of tempera- 

 ture, and would show respiratory changes in an opposite direction. 



Notwithstanding these limitations, which must be borne in 

 mind, the method of perfusion has yielded important results ; it 

 has been shown thereby that tissues have the power of taking up 



i See page 549, 



