[MACLEOD] THE RESPIRATORY CENTRE 101 



B, LXXXIX, 444) that the lactic acid which is produced by a muscu- 

 lar contraction is removed by an oxidative process before the next con- 

 traction takes place, then it is conceivable that in the perm.anent con- 

 traction, to which plastic tonus corresponds, the acid fails to disappear 

 from the muscle so that it overflows into the blood, in which it accumu- 

 lates, since it can no longer be removed by oxidation, and from 

 which it is only gradually excreted. 



In brief, then, the simplest interpretation for the hyperpnœa and 

 final collapse of many decerebrate animals is that it is caused by acute 

 acidosis brought about by an accumulation of lactic acid derived from 

 the permanently contracted extensor m.usculature which is character- 

 istic of this condition. But we do not intend to imply that this hypo- 

 thesis is proven by the observations of the present research. In so far 

 as the results themselves are concerned there can be no doubt as to 

 the reliability and tolerable accuracy of the values given for the carbon 

 dioxide of the alveolar air and blood, but there is a possibility of error 

 in connection with those for the Ph and lactic acid content of blood. 

 The greatest care has been taken in the analyses and they have always 

 been carried out under strictly standardized conditions, but neverthe- 

 less it is possible that the samples of blood on which they were carried 

 out were removed when the animal was already in a moribund con- 

 dition, in which because of failing circulation such changes as were 

 observed are to be expected. To circumvent this possible source of 

 error blood was taken from one of the hyperpnoeic animals (Table IV, 

 No. XXX) while the arterial blood pressure was still above 70 mm. 

 Hg., with the same results. Further observations of a similar type are, 

 however, necessary. 



With regard to the second hypothesis, namely that the organic 

 acid of the blood rises to take the place of the carbonic acid which is 

 blown ofï because of hyperpnœa induced by afferent stumuli acting on 

 a hyperexcitable respiratory centre, little that is definite can be said. 

 In support of this view, however, stands the fact that the animals 

 exhibiting the hyperpnœa were invariably those in which, because of 

 the forward position of the section, there was decided hyperexcit- 

 ability of the nerve centres. 



